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3187 lines
119 KiB
Plaintext
<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.183 2003/06/11 18:01:13 momjian Exp $
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-->
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<Chapter Id="runtime">
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<Title>Server Run-time Environment</Title>
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<Para>
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This chapter discusses how to set up and run the database server
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and the interactions with the operating system.
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</para>
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<sect1 id="postgres-user">
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<title>The <productname>PostgreSQL</productname> User Account</title>
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<indexterm>
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<primary>postgres user</primary>
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</indexterm>
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<para>
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As with any other server daemon that is connected to outside world,
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it is advisable to run <productname>PostgreSQL</productname> under a
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separate user account. This user account should only own the data
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that is managed by the server, and should not be shared with other
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daemons. (For example, using the user <literal>nobody</literal> is a bad
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idea.) It is not advisable to install executables owned by
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this user because compromised systems could then modify their own
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binaries.
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</para>
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<para>
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To add a Unix user account to your system, look for a command
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<command>useradd</command> or <command>adduser</command>. The user
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name <systemitem>postgres</systemitem> is often used but is by no
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means required.
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</para>
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</sect1>
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<sect1 id="creating-cluster">
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<title>Creating a Database Cluster</title>
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<indexterm>
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<primary>database cluster</primary>
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</indexterm>
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<indexterm>
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<primary>data area</primary>
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<see>database cluster</see>
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</indexterm>
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<para>
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Before you can do anything, you must initialize a database storage
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area on disk. We call this a <firstterm>database cluster</firstterm>.
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(<acronym>SQL</acronym> uses the term catalog cluster instead.) A
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database cluster is a collection of databases is accessible by a
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single instance of a running database server. After initialization, a
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database cluster will contain a database named
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<literal>template1</literal>. As the name suggests, this will be used
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as a template for subsequently created databases; it should not be
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used for actual work. (See <xref linkend="managing-databases"> for information
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about creating databases.)
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</para>
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<para>
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In file system terms, a database cluster will be a single directory
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under which all data will be stored. We call this the <firstterm>data
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directory</firstterm> or <firstterm>data area</firstterm>. It is
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completely up to you where you choose to store your data. There is no
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default, although locations such as
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<filename>/usr/local/pgsql/data</filename> or
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<filename>/var/lib/pgsql/data</filename> are popular. To initialize a
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database cluster, use the command <command>initdb</command>, which is
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installed with <productname>PostgreSQL</productname>. The desired
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file system location of your database system is indicated by the
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<option>-D</option> option, for example
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<screen>
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<prompt>$</> <userinput>initdb -D /usr/local/pgsql/data</userinput>
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</screen>
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Note that you must execute this command while logged into the
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<productname>PostgreSQL</productname> user account, which is
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described in the previous section.
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</para>
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<tip>
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<para>
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As an alternative to the <option>-D</option> option, you can set
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the environment variable <envar>PGDATA</envar>.
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<indexterm><primary><envar>PGDATA</envar></primary></indexterm>
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</para>
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</tip>
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<para>
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<command>initdb</command> will attempt to create the directory you
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specify if it does not already exist. It is likely that it will not
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have the permission to do so (if you followed our advice and created
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an unprivileged account). In that case you should create the
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directory yourself (as root) and change the owner to be the
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<productname>PostgreSQL</productname> user. Here is how this might
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be done:
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<screen>
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root# <userinput>mkdir /usr/local/pgsql/data</userinput>
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root# <userinput>chown postgres /usr/local/pgsql/data</userinput>
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root# <userinput>su postgres</userinput>
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postgres$ <userinput>initdb -D /usr/local/pgsql/data</userinput>
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</screen>
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</para>
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<para>
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<command>initdb</command> will refuse to run if the data directory
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looks like it it has already been initialized.</para>
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<para>
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Because the data directory contains all the data stored in the
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database, it is essential that it be secured from unauthorized
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access. <command>initdb</command> therefore revokes access
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permissions from everyone but the
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<productname>PostgreSQL</productname> user.
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</para>
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<para>
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However, while the directory contents are secure, the default
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client authentication setup allows any local user to connect to the
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database and even become the database superuser. If you do not trust
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other local users, we recommend you use <command>initdb</command>'s
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<option>-W</option> or <option>--pwprompt</option> option to assign a
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password to the database superuser. After <command>initdb</command>,
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modify the <filename>pg_hba.conf</filename> file to use <literal>md5</> or
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<literal>password</> instead of <literal>trust</> authentication
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<emphasis>before</> you start the server for the first time. (Other
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approaches include using <literal>ident</literal> authentication or
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file system permissions to restrict connections. See <xref
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linkend="client-authentication"> for more information.)
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</para>
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<para>
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<command>initdb</command> also initializes the default
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locale<indexterm><primary>locale</></> for the database cluster.
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Normally, it will just take the locale settings in the environment
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and apply them to the initialized database. It is possible to
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specify a different locale for the database; more information about
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that can be found in <xref linkend="locale">. The sort order used
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within a particular database cluster is set by
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<command>initdb</command> and cannot be changed later, short of
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dumping all data, rerunning <command>initdb</command>, and
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reloading the data. So it's important to make this choice correctly
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the first time.
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</para>
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</sect1>
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<sect1 id="postmaster-start">
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<title>Starting the Database Server</title>
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<para>
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Before anyone can access the database, you must start the database
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server. The database server program is called
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<command>postmaster</command>.<indexterm><primary>postmaster</></>
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The <command>postmaster</command> must know where to
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find the data it is supposed to use. This is done with the
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<option>-D</option> option. Thus, the simplest way to start the
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server is:
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<screen>
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$ <userinput>postmaster -D /usr/local/pgsql/data</userinput>
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</screen>
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which will leave the server running in the foreground. This must be
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done while logged into the <productname>PostgreSQL</productname> user
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account. Without <option>-D</option>, the server will try to use
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the data directory in the environment variable <envar>PGDATA</envar>.
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If neither of these succeed, it will fail.
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</para>
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<para>
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To start the <command>postmaster</command> in the
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background, use the usual shell syntax:
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<screen>
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$ <userinput>postmaster -D /usr/local/pgsql/data > logfile 2>&1 &</userinput>
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</screen>
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It is an important to store the server's <systemitem>stdout</> and
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<systemitem>stderr</> output somewhere, as shown above. It will help
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for auditing purposes and to diagnose problems. (See <xref
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linkend="logfile-maintenance"> for a more thorough discussion of log
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file handling.)
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</para>
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<para>
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The <command>postmaster</command> also takes a number of other
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command line options. For more information, see the reference page
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and <xref linkend="runtime-config"> below. In particular, in order
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for the server to accept
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TCP/IP<indexterm><primary>TCP/IP</primary></indexterm> connections
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(rather than just Unix-domain socket ones), you must specify the
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<option>-i</option> option.
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</para>
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<para>
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This shell syntax can get tedious quickly. Therefore the shell
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script wrapper
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<command>pg_ctl</command><indexterm><primary>pg_ctl</primary></indexterm>
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is provided to simplify some tasks. For example:
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<programlisting>
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pg_ctl start -l logfile
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</programlisting>
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will start the server in the background and put the output into the
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named log file. The <option>-D</option> option has the same meaning
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here as in the <command>postmaster</command>. <command>pg_ctl</command> is also
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capable of stopping the server.
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</para>
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<para>
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Normally, you will want to start the database server when the
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computer boots. Autostart scripts are operating system-specific.
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There are a few distributed with
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<productname>PostgreSQL</productname> in the
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<filename>contrib/start-scripts</> directory. This may require root
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privileges.
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</para>
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<para>
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Different systems have different conventions for starting up daemons
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at boot time. Many systems have a file
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<filename>/etc/rc.local</filename> or
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<filename>/etc/rc.d/rc.local</filename>. Others use
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<filename>rc.d</> directories. Whatever you do, the server must be
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run by the <productname>PostgreSQL</productname> user account
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<emphasis>and not by root</emphasis> or any other user. Therefore you
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probably should form your commands using <literal>su -c '...'
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postgres</literal>. For example:
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<programlisting>
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su -c 'pg_ctl start -D /usr/local/pgsql/data -l serverlog' postgres
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</programlisting>
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</para>
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<para>
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Here are a few more operating system specific suggestions. (Always
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replace these with the proper installation directory and the user
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name.)
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<itemizedlist>
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<listitem>
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<para>
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For <productname>FreeBSD</productname>, look at the file
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<filename>contrib/start-scripts/freebsd</filename> in the
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<productname>PostgreSQL</productname> source distribution.
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<indexterm><primary>FreeBSD</></>
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</para>
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</listitem>
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<listitem>
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<para>
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On <productname>OpenBSD</productname>, add the following lines
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to the file <filename>/etc/rc.local</filename>:
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<indexterm><primary>OpenBSD</></>
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<programlisting>
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if [ -x /usr/local/pgsql/bin/pg_ctl -a -x /usr/local/pgsql/bin/postmaster ]; then
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su - -c '/usr/local/pgsql/bin/pg_ctl start -l /var/postgresql/log -s' postgres
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echo -n ' postgresql'
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fi
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</programlisting>
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</para>
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</listitem>
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<listitem>
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<para>
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On <productname>Linux</productname> systems either add
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<indexterm><primary>Linux</></>
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<programlisting>
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/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data
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</programlisting>
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to <filename>/etc/rc.d/rc.local</filename> or look at the file
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<filename>contrib/start-scripts/linux</filename> in the
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<productname>PostgreSQL</productname> source distribution.
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</para>
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</listitem>
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<listitem>
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<para>
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On <productname>NetBSD</productname>, either use the
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<productname>FreeBSD</productname> or
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<productname>Linux</productname> start scripts, depending on
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preference. <indexterm><primary>NetBSD</></>
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</para>
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</listitem>
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<listitem>
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<para>
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On <productname>Solaris</productname>, create a file called
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<filename>/etc/init.d/postgresql</filename> that contains
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the following line:
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<indexterm><primary>Solaris</></>
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<programlisting>
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su - postgres -c "/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data"
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</programlisting>
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Then, create a symbolic link to it in <filename>/etc/rc3.d</> as
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<filename>S99postgresql</>.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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While the <command>postmaster</command> is running, its
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<acronym>PID</acronym> is stored in the file
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<filename>postmaster.pid</filename> in the data directory. This is
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used to prevent multiple <command>postmaster</command> processes
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running in the same data directory and can also be used for
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shutting down the <command>postmaster</command> process.
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</para>
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<sect2 id="postmaster-start-failures">
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<title>Server Start-up Failures</title>
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<para>
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There are several common reasons the server might fail to
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start. Check the server's log file, or start it by hand (without
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redirecting standard output or standard error) and see what error
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messages appear. Below we explain some of the most common error
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messages in more detail.
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</para>
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<para>
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<screen>
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FATAL: StreamServerPort: bind() failed: Address already in use
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Is another postmaster already running on port 5432?
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If not, wait a few seconds an retry.
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</screen>
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This usually means just what it suggests: you tried to start
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another <command>postmaster</command> on the same port where one is already running.
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However, if the kernel error message is not <computeroutput>Address
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already in use</computeroutput> or some variant of that, there may
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be a different problem. For example, trying to start a <command>postmaster</command>
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on a reserved port number may draw something like:
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<screen>
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$ <userinput>postmaster -i -p 666</userinput>
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FATAL: StreamServerPort: bind() failed: Permission denied
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Is another postmaster already running on port 666?
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If not, wait a few seconds an retry.
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</screen>
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</para>
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<para>
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A message like
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<screen>
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IpcMemoryCreate: shmget(key=5440001, size=83918612, 01600) failed: Invalid argument
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FATAL 1: ShmemCreate: cannot create region
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</screen>
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probably means your kernel's limit on the size of shared memory is
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smaller than the buffer area <productname>PostgreSQL</productname>
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is trying to create (83918612 bytes in this example). Or it could
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mean that you do not have System-V-style shared memory support
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configured into your kernel at all. As a temporary workaround, you
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can try starting the server with a smaller-than-normal number
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of buffers (<option>-B</option> switch). You will eventually want
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to reconfigure your kernel to increase the allowed shared memory
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size. You may also see this message when trying to start multiple
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servers on the same machine if their total space requested
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exceeds the kernel limit.
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</para>
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<para>
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An error like
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<screen>
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IpcSemaphoreCreate: semget(key=5440026, num=16, 01600) failed: No space left on device
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</screen>
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does <emphasis>not</emphasis> mean you've run out of disk
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space. It means your kernel's limit on the number of <systemitem
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class="osname">System V</> semaphores is smaller than the number
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<productname>PostgreSQL</productname> wants to create. As above,
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you may be able to work around the problem by starting the
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server with a reduced number of allowed connections
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(<option>-N</option> switch), but you'll eventually want to
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increase the kernel limit.
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</para>
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<para>
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If you get an <quote>illegal system call</> error, it is likely that
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shared memory or semaphores are not supported in your kernel at
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all. In that case your only option is to reconfigure the kernel to
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enable these features.
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</para>
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<para>
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Details about configuring <systemitem class="osname">System V</>
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<acronym>IPC</> facilities are given in <xref linkend="sysvipc">.
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</para>
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</sect2>
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<sect2 id="client-connection-problems">
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<title>Client Connection Problems</title>
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<para>
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Although the error conditions possible on the client side are quite
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varied and application-dependent, a few of them might be directly
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related to how the server was started up. Conditions other than
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those shown below should be documented with the respective client
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application.
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</para>
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<para>
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<screen>
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psql: could not connect to server: Connection refused
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Is the server running on host server.joe.com and accepting
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TCP/IP connections on port 5432?
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</screen>
|
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This is the generic <quote>I couldn't find a server to talk
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to</quote> failure. It looks like the above when TCP/IP
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|
communication is attempted. A common mistake is to forget to
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configure the server to allow TCP/IP connections.
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</para>
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<para>
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Alternatively, you'll get this when attempting Unix-domain socket
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communication to a local server:
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<screen>
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psql: could not connect to server: Connection refused
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Is the server running locally and accepting
|
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connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
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</screen>
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</para>
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<para>
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The last line is useful in verifying that the client is trying to
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connect to the right place. If there is in fact no server
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running there, the kernel error message will typically be either
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<computeroutput>Connection refused</computeroutput> or
|
|
<computeroutput>No such file or directory</computeroutput>, as
|
|
illustrated. (It is important to realize that
|
|
<computeroutput>Connection refused</computeroutput> in this context
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|
does <emphasis>not</emphasis> mean that the server got your
|
|
connection request and rejected it. That case will produce a
|
|
different message, as shown in <xref
|
|
linkend="client-authentication-problems">.) Other error messages
|
|
such as <computeroutput>Connection timed out</computeroutput> may
|
|
indicate more fundamental problems, like lack of network
|
|
connectivity.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
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|
|
<sect1 id="runtime-config">
|
|
<Title>Run-time Configuration</Title>
|
|
|
|
<indexterm>
|
|
<primary>configuration</primary>
|
|
<secondary>server</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
There are a lot of configuration parameters that affect the behavior
|
|
of the database system. Here we describe how to set them and the
|
|
following subsections will discuss each in detail.
|
|
</para>
|
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|
|
<para>
|
|
All parameter names are case-insensitive. Every parameter takes a
|
|
value of one of the four types: Boolean, integer, floating point,
|
|
and string. Boolean values are <literal>ON</literal>,
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|
<literal>OFF</literal>, <literal>TRUE</literal>,
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|
<literal>FALSE</literal>, <literal>YES</literal>,
|
|
<literal>NO</literal>, <literal>1</literal>, <literal>0</literal>
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|
(case-insensitive) or any non-ambiguous prefix of these.
|
|
</para>
|
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|
|
<para>
|
|
One way to set these options is to edit the file
|
|
<filename>postgresql.conf</filename> in the data directory. (A
|
|
default file is installed there.) An example of what this file might
|
|
look like is:
|
|
<programlisting>
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# This is a comment
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log_connections = yes
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syslog = 2
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search_path = '$user, public'
|
|
</programlisting>
|
|
As you see, options are one per line. The equal sign between name
|
|
and value is optional. Whitespace is insignificant and blank lines
|
|
are ignored. Hash marks (<literal>#</literal>) introduce comments
|
|
anywhere. Parameter values that are not simple identifiers or
|
|
numbers should be single-quoted.
|
|
</para>
|
|
|
|
<para>
|
|
<indexterm>
|
|
<primary>SIGHUP</primary>
|
|
</indexterm>
|
|
The configuration file is reread whenever the <command>postmaster</command> process receives a
|
|
<systemitem>SIGHUP</> signal (which is most easily sent by means of
|
|
<literal>pg_ctl reload</>). The <command>postmaster</command> also propagates this
|
|
signal to all currently running server processes so that existing
|
|
sessions also get the new value. Alternatively, you can send the
|
|
signal to a single server process directly.
|
|
</para>
|
|
|
|
<para>
|
|
A second way to set these configuration parameters is to give them
|
|
as a command line option to the <command>postmaster</command>, such as:
|
|
<programlisting>
|
|
postmaster -c log_connections=yes -c syslog=2
|
|
</programlisting>
|
|
Command-line options override any conflicting settings in
|
|
<filename>postgresql.conf</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
Occasionally it is also useful to give a command line option to
|
|
one particular session only. The environment variable
|
|
<envar>PGOPTIONS</envar> can be used for this purpose on the
|
|
client side:
|
|
<programlisting>
|
|
env PGOPTIONS='-c geqo=off' psql
|
|
</programlisting>
|
|
(This works for any <application>libpq</>-based client application, not just
|
|
<application>psql</application>.) Note that this won't work for
|
|
options that are fixed when the server is started, such as the port
|
|
number.
|
|
</para>
|
|
|
|
<para>
|
|
Some options can be changed in individual SQL sessions with the
|
|
<command>SET</command> command, for example:
|
|
<screen>
|
|
SET ENABLE_SEQSCAN TO OFF;
|
|
</screen>
|
|
See the SQL command language reference for details on the syntax.
|
|
</para>
|
|
|
|
<para>
|
|
Furthermore, it is possible to assign a set of option settings to
|
|
a user or a database. Whenever a session is started, the default
|
|
settings for the user and database involved are loaded. The
|
|
commands <literal>ALTER DATABASE</literal> and <literal>ALTER
|
|
USER</literal>, respectively, are used to configure these
|
|
settings. Such per-database settings override anything received
|
|
from the <command>postmaster</command> command-line or the
|
|
configuration file, and in turn are overridden by per-user
|
|
settings.
|
|
</para>
|
|
|
|
<para>
|
|
The virtual table <structname>pg_settings</structname> allows
|
|
displaying and updating session run-time parameters. It contains one
|
|
row for each configuration parameter; the columns are shown in
|
|
<xref linkend="runtime-pgsettings-table">. This form allows the
|
|
configuration data to be joined with other tables and have a
|
|
selection criteria applied.
|
|
</para>
|
|
|
|
<para>
|
|
An <command>UPDATE</command> performed on <structname>pg_settings</structname>
|
|
is equivalent to executing the <command>SET</command> command on that named
|
|
parameter. The change only affects the value used by the current session. If
|
|
an <command>UPDATE</command> is issued within a transaction that is later
|
|
aborted, the effects of the <command>UPDATE</command> command disappear when
|
|
the transaction is rolled back. Once the surrounding transaction is
|
|
committed, the effects will persist until the end of the session, unless
|
|
overridden by another <command>UPDATE</command> or <command>SET</command>.
|
|
</para>
|
|
|
|
<table id="runtime-pgsettings-table">
|
|
<title><literal>pg_settings</> Columns</title>
|
|
|
|
<tgroup cols=3>
|
|
<thead>
|
|
<row>
|
|
<entry>Name</entry>
|
|
<entry>Data Type</entry>
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><literal>name</literal></entry>
|
|
<entry><type>text</type></entry>
|
|
<entry>The name of the run-time configuration parameter</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>setting</literal></entry>
|
|
<entry><type>text</type></entry>
|
|
<entry>The current value of the run-time configuration parameter</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<sect2 id="runtime-config-optimizer">
|
|
<title>Planner and Optimizer Tuning</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><varname>CPU_INDEX_TUPLE_COST</varname> (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the query planner's estimate of the cost of processing
|
|
each index tuple during an index scan. This is measured as a
|
|
fraction of the cost of a sequential page fetch.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>CPU_OPERATOR_COST</varname> (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the planner's estimate of the cost of processing each
|
|
operator in a <literal>WHERE</> clause. This is measured as a fraction of
|
|
the cost of a sequential page fetch.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>CPU_TUPLE_COST</varname> (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the query planner's estimate of the cost of processing
|
|
each tuple during a query. This is measured as a fraction of
|
|
the cost of a sequential page fetch.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DEFAULT_STATISTICS_TARGET</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the default statistics target for table columns that have not
|
|
had a column-specific target set via <command>ALTER TABLE SET
|
|
STATISTICS</>. Larger values increase the time needed to do
|
|
<command>ANALYZE</>, but may improve the quality of the planner's
|
|
estimates. The default value is 10.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>EFFECTIVE_CACHE_SIZE</varname> (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the planner's assumption about the effective size of the
|
|
disk cache (that is, the portion of the kernel's disk cache that
|
|
will be used for <productname>PostgreSQL</productname> data
|
|
files). This is measured in disk pages, which are normally 8 kB
|
|
each.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ENABLE_HASHAGG</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of hashed aggregation
|
|
plan types. The default is on. This is used for debugging the query
|
|
planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ENABLE_HASHJOIN</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of hash-join plan
|
|
types. The default is on. This is used for debugging the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>index scan</primary>
|
|
</indexterm>
|
|
|
|
<term><varname>ENABLE_INDEXSCAN</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of index-scan plan
|
|
types. The default is on. This is used to debugging the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ENABLE_MERGEJOIN</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of merge-join plan
|
|
types. The default is on. This is used for debugging the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ENABLE_NESTLOOP</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of nested-loop join
|
|
plans. It's not possible to suppress nested-loop joins entirely,
|
|
but turning this variable off discourages the planner from using
|
|
one if there are other methods available. The default is
|
|
on. This is used for debugging the query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>sequential scan</primary>
|
|
</indexterm>
|
|
|
|
<term><varname>ENABLE_SEQSCAN</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of sequential scan
|
|
plan types. It's not possible to suppress sequential scans
|
|
entirely, but turning this variable off discourages the planner
|
|
from using one if there are other methods available. The
|
|
default is on. This is used for debugging the query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ENABLE_SORT</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of explicit sort
|
|
steps. It's not possible to suppress explicit sorts entirely,
|
|
but turning this variable off discourages the planner from
|
|
using one if there are other methods available. The default
|
|
is on. This is used for debugging the query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ENABLE_TIDSCAN</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of <acronym>TID</> scan plan
|
|
types. The default is on. This is used for debugging the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>FROM_COLLAPSE_LIMIT</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
The planner will merge sub-queries into upper queries if the resulting
|
|
FROM list would have no more than this many items. Smaller values
|
|
reduce planning time but may yield inferior query plans.
|
|
The default is 8. It is usually wise to keep this less than
|
|
<literal>GEQO_THRESHOLD</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>genetic query optimization</primary>
|
|
</indexterm>
|
|
<indexterm>
|
|
<primary>GEQO</primary>
|
|
<see>genetic query optimization</see>
|
|
</indexterm>
|
|
|
|
<term><varname>GEQO</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables genetic query optimization, which is an
|
|
algorithm that attempts to do query planning without exhaustive
|
|
searching. This is on by default. See also the various other
|
|
<varname>GEQO_</varname> settings.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>GEQO_EFFORT</varname> (<type>integer</type>)</term>
|
|
<term><varname>GEQO_GENERATIONS</varname> (<type>integer</type>)</term>
|
|
<term><varname>GEQO_POOL_SIZE</varname> (<type>integer</type>)</term>
|
|
<term><varname>GEQO_RANDOM_SEED</varname> (<type>integer</type>)</term>
|
|
<term><varname>GEQO_SELECTION_BIAS</varname> (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Various tuning parameters for the genetic query optimization
|
|
algorithm: The pool size is the number of individuals in one
|
|
population. Valid values are between 128 and 1024. If it is set
|
|
to 0 (the default) a pool size of 2^(QS+1), where QS is the
|
|
number of <literal>FROM</> items in the query, is taken. The effort is used
|
|
to calculate a default for generations. Valid values are between
|
|
1 and 80, 40 being the default. Generations specifies the number
|
|
of iterations in the algorithm. The number must be a positive
|
|
integer. If 0 is specified then <literal>Effort *
|
|
Log2(PoolSize)</literal> is used. The run time of the algorithm
|
|
is roughly proportional to the sum of pool size and generations.
|
|
The selection bias is the selective pressure within the
|
|
population. Values can be from 1.50 to 2.00; the latter is the
|
|
default. The random seed can be set to get reproducible results
|
|
from the algorithm. If it is set to -1 then the algorithm
|
|
behaves non-deterministically.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>GEQO_THRESHOLD</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Use genetic query optimization to plan queries with at least
|
|
this many <literal>FROM</> items involved. (Note that an outer
|
|
<literal>JOIN</> construct counts as only one <literal>FROM</>
|
|
item.) The default is 11. For simpler queries it is usually best
|
|
to use the deterministic, exhaustive planner, but for queries with
|
|
many tables the deterministic planner takes too long.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>JOIN_COLLAPSE_LIMIT</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
The planner will flatten explicit inner <literal>JOIN</> constructs
|
|
into lists of <literal>FROM</> items whenever a list of no more than
|
|
this many items would result. Usually this is set the same as
|
|
<literal>FROM_COLLAPSE_LIMIT</>. Setting it to 1 prevents any
|
|
flattening of inner <literal>JOIN</>s, allowing explicit
|
|
<literal>JOIN</> syntax to be used to control the join order.
|
|
Intermediate values might be useful to trade off planning time
|
|
against quality of plan.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>RANDOM_PAGE_COST</varname> (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the query planner's estimate of the cost of a
|
|
nonsequentially fetched disk page. This is measured as a
|
|
multiple of the cost of a sequential page fetch. A higher
|
|
value makes it more likely a sequential scan will be used,
|
|
a lower value makes it more likely an index scan will be used.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<note>
|
|
<para>
|
|
Unfortunately, there is no well-defined method for determining
|
|
ideal values for the family of <quote>cost</quote> variables that
|
|
were just described. You are encouraged to experiment and share
|
|
your findings.
|
|
</para>
|
|
</note>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="logging">
|
|
<title>Logging and Debugging</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><varname>CLIENT_MIN_MESSAGES</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This controls which message levels are send to the client.
|
|
client. Valid values are <literal>DEBUG5</>,
|
|
<literal>DEBUG4</>, <literal>DEBUG3</>, <literal>DEBUG2</>,
|
|
<literal>DEBUG1</>, <literal>LOG</>, <literal>NOTICE</>,
|
|
<literal>WARNING</>, and <literal>ERROR</>. Each level
|
|
includes all the levels that follow it. The later the level,
|
|
the fewer messages are sent. The default is
|
|
<literal>NOTICE</>. Note that <literal>LOG</> has a different
|
|
rank here than in <literal>LOG_MIN_MESSAGES</>.
|
|
</para>
|
|
|
|
<para>
|
|
Here is a list of the various message types:
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>DEBUG[1-5]</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Provides information for use by developers.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>INFO</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Provides information implicitly requested by the user,
|
|
e.g., during <command>VACUUM VERBOSE</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>NOTICE</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Provides information that may be helpful to users, e.g.,
|
|
truncation of long identifiers and the creation of indexes as part
|
|
of primary keys.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>WARNING</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Provides warnings to the user, e.g., <command>COMMIT</>
|
|
outside a transaction block.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>ERROR</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Reports an error that caused the current transaction to abort.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>LOG</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Reports information of interest to administrators, e.g.,
|
|
checkpoint activity.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>FATAL</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Reports an error that caused the current session to abort.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>PANIC</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Reports an error that caused all sessions to abort.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DEBUG_ASSERTIONS</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Turns on various assertion checks. This is a debugging aid. If
|
|
you are experiencing strange problems or crashes you might want
|
|
to turn this on, as it might expose programming mistakes. To use
|
|
this option, the macro <literal>USE_ASSERT_CHECKING</literal>
|
|
must be defined when <productname>PostgreSQL</productname> is
|
|
built (accomplished by the <command>configure</command> option
|
|
<option>--enable-cassert</option>). Note that
|
|
<literal>DEBUG_ASSERTIONS</literal> defaults to on if
|
|
<productname>PostgreSQL</productname> has been built with
|
|
assertions enabled.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DEBUG_PRINT_PARSE</varname> (<type>boolean</type>)</term>
|
|
<term><varname>DEBUG_PRINT_REWRITTEN</varname> (<type>boolean</type>)</term>
|
|
<term><varname>DEBUG_PRINT_PLAN</varname> (<type>boolean</type>)</term>
|
|
<term><varname>DEBUG_PRETTY_PRINT</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
These options enable various debugging output to be sent to the
|
|
client or server log. For each executed query, they print the resulting
|
|
parse tree, the query rewriter output, or the execution plan.
|
|
<option>DEBUG_PRETTY_PRINT</option> indents these displays to
|
|
produce a more readable but much longer output format.
|
|
<option>CLIENT_MIN_MESSAGES</option> or <option>LOG_MIN_MESSAGES</option>
|
|
must be <literal>DEBUG1</literal> or lower to send output to the client
|
|
or server logs.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>EXPLAIN_PRETTY_PRINT</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Determines whether <command>EXPLAIN VERBOSE</> uses the indented
|
|
or non-indented format for displaying detailed query-tree dumps.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_HOSTNAME</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
By default, connection logs only show the IP address of the
|
|
connecting host. If you want it to show the host name you can
|
|
turn this on, but depending on your host name resolution setup
|
|
it might impose a non-negligible performance penalty. This
|
|
option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_CONNECTIONS</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This outputs a line to the server logs detailing each successful
|
|
connection. This is off by default, although it is probably very
|
|
useful. This option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> configuration file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_DURATION</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Causes the duration of every completed statement to be logged.
|
|
To use this option, enable <varname>LOG_STATEMENT</> and
|
|
<varname>LOG_PID</> so you can link the statement to the
|
|
duration using the process ID.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_MIN_DURATION_STATEMENT</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets a minimum statement execution time (in milliseconds)
|
|
above which a statement will be logged. All SQL statements
|
|
that run longer than the time specified will be logged together
|
|
with the duration, in seconds. The default is <literal>0</literal>
|
|
(turning this feature off). For example, if you set it
|
|
to <literal>250</literal> then all SQL statements that run longer
|
|
than 250ms will be logged along with the duration. Enabling this
|
|
option can be useful in tracking down unoptimized queries in
|
|
your applications.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_MIN_ERROR_STATEMENT</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Controls whether or not the SQL statement that causes an error
|
|
condition will also be recorded in the server log. All SQL
|
|
statements that cause an error of the specified level, or a
|
|
higher level, are logged. The default is
|
|
<literal>PANIC</literal> (effectively turning this feature
|
|
off). Valid values are <literal>DEBUG5</literal>,
|
|
<literal>DEBUG4</literal>, <literal>DEBUG3</literal>,
|
|
<literal>DEBUG2</literal>, <literal>DEBUG1</literal>,
|
|
<literal>INFO</literal>, <literal>NOTICE</literal>,
|
|
<literal>WARNING</literal>, <literal>ERROR</literal>,
|
|
<literal>FATAL</literal>, and <literal>PANIC</literal>. For
|
|
example, if you set this to <literal>ERROR</literal> then all
|
|
SQL statements causing errors, fatal errors, or panics will be
|
|
logged. Enabling this option can be helpful in tracking down
|
|
the source of any errors that appear in the server log.
|
|
</para>
|
|
|
|
<para>
|
|
It is recommended you enable <varname>LOG_PID</varname> as well
|
|
so you can more easily match the error statement with the error
|
|
message.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_MIN_MESSAGES</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This controls which message levels are written to the server
|
|
log. Valid values are <literal>DEBUG5</>, <literal>DEBUG4</>,
|
|
<literal>DEBUG3</>, <literal>DEBUG2</>, <literal>DEBUG1</>,
|
|
<literal>INFO</>, <literal>NOTICE</>, <literal>WARNING</>,
|
|
<literal>ERROR</>, <literal>LOG</>, <literal>FATAL</>, and
|
|
<literal>PANIC</>. Each level includes all the levels that
|
|
follow it. The later the level, the fewer messages are sent
|
|
to the log. The default is <literal>NOTICE</>. Note that
|
|
<literal>LOG</> has a different rank here than in
|
|
<literal>CLIENT_MIN_MESSAGES</>. Also see that section for an
|
|
explanation of the various values.
|
|
</para>
|
|
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_PID</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Prefixes each message in the server log file with the process ID of
|
|
the server process. This is useful to sort out which messages
|
|
pertain to which connection. The default is off. This parameter
|
|
does not affect messages logged via <application>syslog</>, which always contain
|
|
the process ID.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_STATEMENT</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Causes each SQL statement to be logged.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_TIMESTAMP</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Prefixes each server log message with a time stamp. The default
|
|
is off.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_STATEMENT_STATS</varname> (<type>boolean</type>)</term>
|
|
<term><varname>LOG_PARSER_STATS</varname> (<type>boolean</type>)</term>
|
|
<term><varname>LOG_PLANNER_STATS</varname> (<type>boolean</type>)</term>
|
|
<term><varname>LOG_EXECUTOR_STATS</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
For each query, write performance statistics of the respective
|
|
module to the server log. This is a crude profiling
|
|
instrument.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LOG_SOURCE_PORT</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Shows the outgoing port number of the connecting host in the
|
|
connection log messages. You could trace back the port number
|
|
to find out what user initiated the connection. Other than
|
|
that, it's pretty useless and therefore off by default. This
|
|
option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>STATS_COMMAND_STRING</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables the collection of statistics on the currently
|
|
executing command of each session, along with the time at
|
|
which that command began execution. This option is off by
|
|
default. Note that even when enabled, this information is not
|
|
visible to all users, only to superusers and the user owning
|
|
the session being reported on; so it should not represent a
|
|
security risk. This data can be accessed via the
|
|
<structname>pg_stat_activity</structname> system view; refer
|
|
to <xref linkend="monitoring"> for more information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>STATS_BLOCK_LEVEL</varname> (<type>boolean</type>)</term>
|
|
<term><varname>STATS_ROW_LEVEL</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
These enable the collection of block-level and row-level statistics
|
|
on database activity, respectively. These options are off by
|
|
default. This data can be accessed via the
|
|
<structname>pg_stat</structname> and
|
|
<structname>pg_statio</structname> family of system views;
|
|
refer to <xref linkend="monitoring"> for more information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>STATS_RESET_ON_SERVER_START</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If on, collected statistics are zeroed out whenever the server
|
|
is restarted. If off, statistics are accumulated across server
|
|
restarts. The default is on. This option can only be set at
|
|
server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>STATS_START_COLLECTOR</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Controls whether the server should start the
|
|
statistics-collection subprocess. This is on by default, but
|
|
may be turned off if you know you have no interest in
|
|
collecting statistics. This option can only be set at server
|
|
start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SYSLOG</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
<productname>PostgreSQL</productname> allows the use of
|
|
<systemitem>syslog</systemitem> for logging. If this option is
|
|
set to 1, messages go both to <systemitem>syslog</> and the
|
|
standard output. A setting of 2 sends output only to
|
|
<systemitem>syslog</>. (Some messages will still go to the
|
|
standard output/error.) The default is 0, which means
|
|
<systemitem>syslog</> is off. This option must be set at server
|
|
start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SYSLOG_FACILITY</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This option determines the <application>syslog</application>
|
|
<quote>facility</quote> to be used when logging via
|
|
<application>syslog</application> is enabled. You may choose
|
|
from <literal>LOCAL0</>, <literal>LOCAL1</>,
|
|
<literal>LOCAL2</>, <literal>LOCAL3</>, <literal>LOCAL4</>,
|
|
<literal>LOCAL5</>, <literal>LOCAL6</>, <literal>LOCAL7</>;
|
|
the default is <literal>LOCAL0</>. See also the
|
|
documentation of your system's
|
|
<application>syslog</application>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SYSLOG_IDENT</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If logging to <application>syslog</> is enabled, this option
|
|
determines the program name used to identify
|
|
<productname>PostgreSQL</productname> messages in
|
|
<application>syslog</application> log messages. The default is
|
|
<literal>postgres</literal>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>TRACE_NOTIFY</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Generates a great amount of debugging output for the
|
|
<command>LISTEN</command> and <command>NOTIFY</command>
|
|
commands.
|
|
<option>CLIENT_MIN_MESSAGES</option> or <option>LOG_MIN_MESSAGES</option>
|
|
must be <literal>DEBUG1</literal> or lower to send output to the client
|
|
or server logs.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="runtime-config-general">
|
|
<title>General Operation</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><varname>AUSTRALIAN_TIMEZONES</varname> (<type>boolean</type>)</term>
|
|
<indexterm><primary>Australian time zones</></>
|
|
<listitem>
|
|
<para>
|
|
If set to true, <literal>ACST</literal>,
|
|
<literal>CST</literal>, <literal>EST</literal>, and
|
|
<literal>SAT</literal> are interpreted as Australian time
|
|
zones rather than as North/South American time zones and
|
|
Saturday. The default is false.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>AUTHENTICATION_TIMEOUT</varname> (<type>integer</type>)</term>
|
|
<indexterm><primary>timeout</><secondary>authentication</></indexterm>
|
|
<listitem>
|
|
<para>
|
|
Maximum time to complete client authentication, in seconds. If a
|
|
would-be client has not completed the authentication protocol in
|
|
this much time, the server breaks the connection. This prevents
|
|
hung clients from occupying a connection indefinitely. This
|
|
option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>CLIENT_ENCODING</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>character set encoding</></>
|
|
<listitem>
|
|
<para>
|
|
Sets the client-side encoding (character set).
|
|
The default is to use the database encoding.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DATESTYLE</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>date style</></>
|
|
<listitem>
|
|
<para>
|
|
Sets the display format for date and time values, as well as
|
|
the rules for interpreting ambiguous date input values. See
|
|
<xref linkend="datatype-datetime"> for more information. The
|
|
default is <literal>ISO, US</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DB_USER_NAMESPACE</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This allows per-database user names. It is off by default.
|
|
</para>
|
|
|
|
<para>
|
|
If this is on, you should create users as <literal>username@dbname</>.
|
|
When <literal>username</> is passed by a connecting client,
|
|
<literal>@</> and the database name is appended to the user
|
|
name and that database-specific user name is looked up by the
|
|
server. Note that when you create users with names containing
|
|
<literal>@</> within the SQL environment, you will need to
|
|
quote the user name.
|
|
</para>
|
|
|
|
<para>
|
|
With this option enabled, you can still create ordinary global
|
|
users. Simply append <literal>@</> when specifying the user
|
|
name in the client. The <literal>@</> will be stripped off
|
|
before the user name is looked up by the server.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
This feature is intended as a temporary measure until a
|
|
complete solution is found. At that time, this option will
|
|
be removed.
|
|
</para>
|
|
</note>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>deadlock</primary>
|
|
<secondary>timeout</secondary>
|
|
</indexterm>
|
|
<indexterm>
|
|
<primary>timeout</primary>
|
|
<secondary>deadlock</secondary>
|
|
</indexterm>
|
|
|
|
<term><varname>DEADLOCK_TIMEOUT</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This is the amount of time, in milliseconds, to wait on a lock
|
|
before checking to see if there is a deadlock condition. The
|
|
check for deadlock is relatively slow, so the server doesn't run
|
|
it every time it waits for a lock. We (optimistically?) assume
|
|
that deadlocks are not common in production applications and
|
|
just wait on the lock for a while before starting the check for a
|
|
deadlock. Increasing this value reduces the amount of time
|
|
wasted in needless deadlock checks, but slows down reporting of
|
|
real deadlock errors. The default is 1000 (i.e., one second),
|
|
which is probably about the smallest value you would want in
|
|
practice. On a heavily loaded server you might want to raise it.
|
|
Ideally the setting should exceed your typical transaction time,
|
|
so as to improve the odds that a lock will be released before
|
|
the waiter decides to check for deadlock.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>transaction isolation level</primary>
|
|
</indexterm>
|
|
|
|
<term><varname>DEFAULT_TRANSACTION_ISOLATION</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Each SQL transaction has an isolation level, which can be either
|
|
<quote>read committed</quote> or <quote>serializable</quote>.
|
|
This parameter controls the default isolation level of each new
|
|
transaction. The default is <quote>read committed</quote>.
|
|
</para>
|
|
|
|
<para>
|
|
Consult <xref linkend="mvcc"> and <xref linkend="sql-set-transaction"> for more
|
|
information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>read-only transaction</primary>
|
|
</indexterm>
|
|
|
|
<term><varname>DEFAULT_TRANSACTION_READ_ONLY</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
A read-only SQL transaction cannot alter non-temporary tables.
|
|
This parameter controls the default read-only status of each new
|
|
transaction. The default is false (read/write).
|
|
</para>
|
|
|
|
<para>
|
|
Consult <xref linkend="sql-set-transaction"> for more information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DYNAMIC_LIBRARY_PATH</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>dynamic_library_path</></>
|
|
<indexterm><primary>dynamic loading</></>
|
|
<listitem>
|
|
<para>
|
|
If a dynamically loadable module needs to be opened and the
|
|
specified name does not have a directory component (i.e. the
|
|
name does not contain a slash), the system will search this
|
|
path for the specified file. (The name that is used is the
|
|
name specified in the <command>CREATE FUNCTION</command> or
|
|
<command>LOAD</command> command.)
|
|
</para>
|
|
|
|
<para>
|
|
The value for <varname>DYNAMIC_LIBRARY_PATH</varname> has to be a colon-separated
|
|
list of absolute directory names. If a directory name starts
|
|
with the special value <literal>$libdir</literal>, the
|
|
compiled-in <productname>PostgreSQL</productname> package
|
|
library directory is substituted. This where the modules
|
|
provided by the <productname>PostgreSQL</productname>
|
|
distribution are installed. (Use <literal>pg_config
|
|
--pkglibdir</literal> to print the name of this directory.) For
|
|
example:
|
|
<programlisting>
|
|
dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
The default value for this parameter is
|
|
<literal>'$libdir'</literal>. If the value is set to an empty
|
|
string, the automatic path search is turned off.
|
|
</para>
|
|
|
|
<para>
|
|
This parameter can be changed at run time by superusers, but a
|
|
setting done that way will only persist until the end of the
|
|
client connection, so this method should be reserved for
|
|
development purposes. The recommended way to set this parameter
|
|
is in the <filename>postgresql.conf</filename> configuration
|
|
file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>significant digits</primary>
|
|
</indexterm>
|
|
<indexterm>
|
|
<primary>display</primary>
|
|
<secondary>of float numbers</secondary>
|
|
</indexterm>
|
|
|
|
<term><varname>EXTRA_FLOAT_DIGITS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This parameter adjusts the number of digits displayed for
|
|
floating-point values, including <type>float4</>, <type>float8</>,
|
|
and geometric data types. The parameter value is added to the
|
|
standard number of digits (<literal>FLT_DIG</> or <literal>DBL_DIG</>
|
|
as appropriate). The value can be set as high as 2, to include
|
|
partially-significant digits; this is especially useful for dumping
|
|
float data that needs to be restored exactly. Or it can be set
|
|
negative to suppress unwanted digits.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>KRB_SERVER_KEYFILE</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the location of the Kerberos server key file. See
|
|
<xref linkend="kerberos-auth"> for details.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>fsync</primary>
|
|
</indexterm>
|
|
|
|
<term><varname>FSYNC</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If this option is on, the <productname>PostgreSQL</> server
|
|
will use the <function>fsync()</> system call in several places
|
|
to make sure that updates are physically written to disk. This
|
|
insures that a database cluster will recover to a
|
|
consistent state after an operating system or hardware crash.
|
|
(Crashes of the database server itself are <emphasis>not</>
|
|
related to this.)
|
|
</para>
|
|
|
|
<para>
|
|
However, this operation does slow down
|
|
<productname>PostgreSQL</> because at transaction commit it has
|
|
wait for the operating system to flush the write-ahead log.
|
|
Without <function>fsync</>, the operating system is allowed to
|
|
do its best in buffering, sorting, and delaying writes, which
|
|
can considerably increase performance. However, if the system
|
|
crashes, the results of the last few committed transactions may
|
|
be lost in part or whole. In the worst case, unrecoverable data
|
|
corruption may occur.
|
|
</para>
|
|
|
|
<para>
|
|
For the above reasons, everyone can decide for himself what to
|
|
do with the <varname>fsync</> option. Some administrators
|
|
always leave it off, some turn it off only for bulk loads,
|
|
where there is a clear restart point if something goes wrong,
|
|
and some leave it on just to be on the safe side. The default
|
|
is on so that you are on the safe side. If you trust your
|
|
operating system, your hardware, and your utility company (or
|
|
better your battery backup), you can consider disabling
|
|
<varname>fsync</varname>.
|
|
</para>
|
|
|
|
<para>
|
|
It should be noted that the performance penalty of having
|
|
<varname>fsync</> on is considerably less in
|
|
<productname>PostgreSQL</> version 7.1 and later. If you
|
|
previously suppressed <function>fsync</> for performance
|
|
reasons, you may wish to reconsider your choice.
|
|
</para>
|
|
|
|
<para>
|
|
This option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LC_MESSAGES</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the language in which messages are displayed. Acceptable
|
|
values are system-dependent; see <xref linkend="locale"> for
|
|
more information. If this variable is set to the empty string
|
|
(which is the default) then the value is inherited from the
|
|
execution environment of the server in a system-dependent way.
|
|
</para>
|
|
|
|
<para>
|
|
On some systems, this locale category does not exist. Setting
|
|
this variable will still work, but there will be no effect.
|
|
Also, there is a chance that no translated messages for the
|
|
desired language exist. In that case you will continue to see
|
|
the English messages.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LC_MONETARY</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the locale to use for formatting monetary amounts, for
|
|
example with the <function>to_char</function> family of
|
|
functions. Acceptable values are system-dependent; see <xref
|
|
linkend="locale"> for more information. If this variable is
|
|
set to the empty string (which is the default) then the value
|
|
is inherited from the execution environment of the server in a
|
|
system-dependent way.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LC_NUMERIC</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the locale to use for formatting numbers, for example
|
|
with the <function>to_char()</function> family of
|
|
functions. Acceptable values are system-dependent; see <xref
|
|
linkend="locale"> for more information. If this variable is
|
|
set to the empty string (which is the default) then the value
|
|
is inherited from the execution environment of the server in a
|
|
system-dependent way.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LC_TIME</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the locale to use for formatting date and time values.
|
|
(Currently, this setting does nothing, but it may in the
|
|
future.) Acceptable values are system-dependent; see <xref
|
|
linkend="locale"> for more information. If this variable is
|
|
set to the empty string (which is the default) then the value
|
|
is inherited from the execution environment of the server in a
|
|
system-dependent way.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>MAX_CONNECTIONS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Determines the maximum number of concurrent connections to the
|
|
database server. The default is 32 (unless altered while
|
|
building the server). This parameter can only be set at server
|
|
start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>MAX_EXPR_DEPTH</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the maximum expression nesting depth of the parser. The
|
|
default value is high enough for any normal query, but you can
|
|
raise it if needed. (But if you raise it too high, you run
|
|
the risk of server crashes due to stack overflow.)
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>MAX_FILES_PER_PROCESS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the maximum number of simultaneously open files allowed to each
|
|
server subprocess. The default is 1000. The limit actually used
|
|
by the code is the smaller of this setting and the result of
|
|
<literal>sysconf(_SC_OPEN_MAX)</literal>. Therefore, on systems
|
|
where <function>sysconf</> returns a reasonable limit, you don't
|
|
need to worry about this setting. But on some platforms
|
|
(notably, most BSD systems), <function>sysconf</> returns a
|
|
value that is much larger than the system can really support
|
|
when a large number of processes all try to open that many
|
|
files. If you find yourself seeing <quote>Too many open files</>
|
|
failures, try reducing this setting. This option can only be set
|
|
at server start or in the <filename>postgresql.conf</filename>
|
|
configuration file; if changed in the configuration file, it
|
|
only affects subsequently-started server subprocesses.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>MAX_FSM_PAGES</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the maximum number of disk pages for which free space will
|
|
be tracked in the shared free-space map. Six bytes of shared memory
|
|
are consumed for each page slot. This setting must be more than
|
|
16 * <varname>max_fsm_relations</varname>. The default is 20000.
|
|
This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>MAX_FSM_RELATIONS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the maximum number of relations (tables and indexes) for which
|
|
free space will be tracked in the shared free-space map. Roughly
|
|
fifty bytes of shared memory are consumed for each slot.
|
|
The default is 1000.
|
|
This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>MAX_LOCKS_PER_TRANSACTION</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
The shared lock table is sized on the assumption that at most
|
|
<varname>max_locks_per_transaction</> *
|
|
<varname>max_connections</varname> distinct objects will need to
|
|
be locked at any one time. The default, 64, has historically
|
|
proven sufficient, but you might need to raise this value if you
|
|
have clients that touch many different tables in a single
|
|
transaction. This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>PASSWORD_ENCRYPTION</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
When a password is specified in <command>CREATE USER</> or
|
|
<command>ALTER USER</> without writing either <literal>ENCRYPTED</> or
|
|
<literal>UNENCRYPTED</>, this option determines whether the password is to be
|
|
encrypted. The default is on (encrypt the password).
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>PORT</varname> (<type>integer</type>)</term>
|
|
<indexterm><primary>port</></>
|
|
<listitem>
|
|
<para>
|
|
The TCP port the server listens on; 5432 by default. This
|
|
option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>PRELOAD_LIBRARIES</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>preload_libraries</></>
|
|
<listitem>
|
|
<para>
|
|
This variable specifies one or more shared libraries that are
|
|
to be preloaded at server start. An initialization function
|
|
can also be optionally specified by adding a colon followed by
|
|
the name of the initialization function after the library
|
|
name. For example
|
|
<literal>'$libdir/mylib:init_mylib'</literal> would cause
|
|
<literal>mylib</> to be preloaded and <literal>init_mylib</>
|
|
to be executed. If more than one library is to be loaded, they
|
|
must be delimited with a comma.
|
|
</para>
|
|
|
|
<para>
|
|
If <literal>mylib</> is not found, the server will fail to
|
|
start. However, if <literal>init_mylib</> is not found,
|
|
<literal>mylib</> will still be preloaded without executing
|
|
the initialization function.
|
|
</para>
|
|
|
|
<para>
|
|
By preloading a shared library (and initializing it if
|
|
applicable), the library startup time is avoided when the
|
|
library is first used.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>REGEX_FLAVOR</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>regular expressions</></>
|
|
<listitem>
|
|
<para>
|
|
The regular expression <quote>flavor</> can be set to
|
|
<literal>advanced</>, <literal>extended</>, or <literal>basic</>.
|
|
The usual default is <literal>advanced</>. The <literal>extended</>
|
|
setting may be useful for exact backwards compatibility with
|
|
pre-7.4 releases of <productname>PostgreSQL</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SEARCH_PATH</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>search_path</></>
|
|
<indexterm><primary>path</><secondary>for schemas</></>
|
|
<listitem>
|
|
<para>
|
|
This variable specifies the order in which schemas are searched
|
|
when an object (table, data type, function, etc.) is referenced by a
|
|
simple name with no schema component. When there are objects of
|
|
identical names in different schemas, the one found first
|
|
in the search path is used. An object that is not in any of the
|
|
schemas in the search path can only be referenced by specifying
|
|
its containing schema with a qualified (dotted) name.
|
|
</para>
|
|
|
|
<para>
|
|
The value for <varname>search_path</varname> has to be a comma-separated
|
|
list of schema names. If one of the list items is
|
|
the special value <literal>$user</literal>, then the schema
|
|
having the name returned by <function>SESSION_USER</> is substituted, if there
|
|
is such a schema. (If not, <literal>$user</literal> is ignored.)
|
|
</para>
|
|
|
|
<para>
|
|
The system catalog schema, <literal>pg_catalog</>, is always
|
|
searched, whether it is mentioned in the path or not. If it is
|
|
mentioned in the path then it will be searched in the specified
|
|
order. If <literal>pg_catalog</> is not in the path then it will
|
|
be searched <emphasis>before</> searching any of the path items.
|
|
It should also be noted that the temporary-table schema,
|
|
<literal>pg_temp_<replaceable>nnn</></>, is implicitly searched before any of
|
|
these.
|
|
</para>
|
|
|
|
<para>
|
|
When objects are created without specifying a particular target
|
|
schema, they will be placed in the first schema listed
|
|
in the search path. An error is reported if the search path is
|
|
empty.
|
|
</para>
|
|
|
|
<para>
|
|
The default value for this parameter is
|
|
<literal>'$user, public'</literal> (where the second part will be
|
|
ignored if there is no schema named <literal>public</>).
|
|
This supports shared use of a database (where no users
|
|
have private schemas, and all share use of <literal>public</>),
|
|
private per-user schemas, and combinations of these. Other
|
|
effects can be obtained by altering the default search path
|
|
setting, either globally or per-user.
|
|
</para>
|
|
|
|
<para>
|
|
The current effective value of the search path can be examined
|
|
via the SQL function <function>current_schemas()</>. This is not
|
|
quite the same as examining the value of
|
|
<varname>search_path</varname>, since <function>current_schemas()</>
|
|
shows how the requests appearing in <varname>search_path</varname>
|
|
were resolved.
|
|
</para>
|
|
|
|
<para>
|
|
For more information on schema handling, see <xref linkend="ddl-schemas">.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SHARED_BUFFERS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the number of shared memory buffers used by the database
|
|
server. The default is 64. Each buffer is typically 8192
|
|
bytes. This must be greater than 16, as well as at least twice
|
|
the value of <varname>MAX_CONNECTIONS</varname>; however, a
|
|
higher value can often improve performance.
|
|
Values of a few thousand are recommended
|
|
for production installations. This option can only be set at
|
|
server start.
|
|
</para>
|
|
|
|
<para>
|
|
Increasing this parameter may cause <productname>PostgreSQL</>
|
|
to request more <systemitem class="osname">System V</> shared
|
|
memory than your operating system's default configuration
|
|
allows. See <xref linkend="sysvipc"> for information on how to
|
|
adjust these parameters, if necessary.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SILENT_MODE</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Runs the server silently. If this option is set, the server
|
|
will automatically run in background and any controlling terminals
|
|
are disassociated. Thus, no messages are written to standard
|
|
output or standard error (same effect as <command>postmaster</>'s <option>-S</option>
|
|
option). Unless some logging system such as
|
|
<application>syslog</> is enabled, using this option is
|
|
discouraged since it makes it impossible to see error messages.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SORT_MEM</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the amount of memory to be used by internal sort operations and
|
|
hash tables before switching to temporary disk files. The value is
|
|
specified in kilobytes, and defaults to 1024 kilobytes (1 MB).
|
|
Note that for a complex query, several sort or hash operations might be
|
|
running in parallel; each one will be allowed to use as much memory
|
|
as this value specifies before it starts to put data into temporary
|
|
files. Also, several running sessions could be doing
|
|
sort operations simultaneously. So the total memory used could be many
|
|
times the value of <varname>SORT_MEM</varname>. Sort operations are used
|
|
by <literal>ORDER BY</>, merge joins, and <command>CREATE INDEX</>.
|
|
Hash tables are used in hash joins, hash-based aggregation, and
|
|
hash-based processing of <literal>IN</> subqueries.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SQL_INHERITANCE</varname> (<type>boolean</type>)</term>
|
|
<indexterm><primary>inheritance</></>
|
|
<listitem>
|
|
<para>
|
|
This controls the inheritance semantics, in particular whether
|
|
subtables are included by various commands by default. They were
|
|
not included in versions prior to 7.1. If you need the old
|
|
behavior you can set this variable to off, but in the long run
|
|
you are encouraged to change your applications to use the
|
|
<literal>ONLY</literal> key word to exclude subtables. See
|
|
<xref linkend="sql"> for more information about inheritance.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>SSL</primary>
|
|
</indexterm>
|
|
|
|
<term><varname>SSL</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables <acronym>SSL</> connections. Please read
|
|
<xref linkend="ssl-tcp"> before using this. The default
|
|
is off.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>STATEMENT_TIMEOUT</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Aborts any statement that takes over the specified number of
|
|
milliseconds. A value of zero turns off the timer.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SUPERUSER_RESERVED_CONNECTIONS</varname>
|
|
(<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Determines the number of <quote>connection slots</quote> that
|
|
are reserved for connections by <productname>PostgreSQL</>
|
|
superusers. At most <varname>max_connections</> connections can
|
|
ever be active simultaneously. Whenever the number of active
|
|
concurrent connections is at least <varname>max_connections</> minus
|
|
<varname>superuser_reserved_connections</varname>, new connections
|
|
will be accepted only for superusers.
|
|
</para>
|
|
|
|
<para>
|
|
The default value is 2. The value must be less than the value of
|
|
<varname>max_connections</varname>. This parameter can only be
|
|
set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>TCPIP_SOCKET</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If this is true, then the server will accept TCP/IP connections.
|
|
Otherwise only local Unix domain socket connections are
|
|
accepted. It is off by default. This option can only be set at
|
|
server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>TIMEZONE</varname> (<type>string</type>)</term>
|
|
<indexterm><primary>time zone</></>
|
|
<listitem>
|
|
<para>
|
|
Sets the time zone for displaying and interpreting time
|
|
stamps. The default is to use whatever the system environment
|
|
specifies as the time zone. See <xref
|
|
linkend="datatype-datetime"> for more information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>TRANSFORM_NULL_EQUALS</varname> (<type>boolean</type>)</term>
|
|
<indexterm><primary>IS NULL</></>
|
|
<listitem>
|
|
<para>
|
|
When turned on, expressions of the form
|
|
<literal><replaceable>expr</> = NULL</literal> (or <literal>NULL
|
|
= <replaceable>expr</></literal>) are treated as
|
|
<literal><replaceable>expr</> IS NULL</literal>, that is, they
|
|
return true if <replaceable>expr</> evaluates to the null value,
|
|
and false otherwise. The correct behavior of
|
|
<literal><replaceable>expr</> = NULL</literal> is to always
|
|
return null (unknown). Therefore this option defaults to off.
|
|
</para>
|
|
|
|
<para>
|
|
However, filtered forms in <productname>Microsoft
|
|
Access</productname> generate queries that appear to use
|
|
<literal><replaceable>expr</> = NULL</literal> to test for
|
|
null values, so if you use that interface to access the database you
|
|
might want to turn this option on. Since expressions of the
|
|
form <literal><replaceable>expr</> = NULL</literal> always
|
|
return the null value (using the correct interpretation) they are not
|
|
very useful and do not appear often in normal applications, so
|
|
this option does little harm in practice. But new users are
|
|
frequently confused about the semantics of expressions
|
|
involving null values, so this option is not on by default.
|
|
</para>
|
|
|
|
<para>
|
|
Note that this option only affects the literal <literal>=</>
|
|
operator, not other comparison operators or other expressions
|
|
that are computationally equivalent to some expression
|
|
involving the equals operator (such as <literal>IN</literal>).
|
|
Thus, this option is not a general fix for bad programming.
|
|
</para>
|
|
|
|
<para>
|
|
Refer to <xref linkend="functions-comparison"> for related information.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>UNIX_SOCKET_DIRECTORY</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the directory of the Unix-domain socket on which the
|
|
server is to listen for
|
|
connections from client applications. The default is normally
|
|
<filename>/tmp</filename>, but can be changed at build time.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>UNIX_SOCKET_GROUP</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the group owner of the Unix domain socket. (The owning
|
|
user of the socket is always the user that starts the
|
|
server.) In combination with the option
|
|
<varname>UNIX_SOCKET_PERMISSIONS</varname> this can be used as
|
|
an additional access control mechanism for this socket type.
|
|
By default this is the empty string, which uses the default
|
|
group for the current user. This option can only be set at
|
|
server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>UNIX_SOCKET_PERMISSIONS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the access permissions of the Unix domain socket. Unix
|
|
domain sockets use the usual Unix file system permission set.
|
|
The option value is expected to be an numeric mode
|
|
specification in the form accepted by the
|
|
<function>chmod</function> and <function>umask</function>
|
|
system calls. (To use the customary octal format the number
|
|
must start with a <literal>0</literal> (zero).)
|
|
</para>
|
|
|
|
<para>
|
|
The default permissions are <literal>0777</literal>, meaning
|
|
anyone can connect. Reasonable alternatives are
|
|
<literal>0770</literal> (only user and group, see also under
|
|
<varname>UNIX_SOCKET_GROUP</varname>) and <literal>0700</literal>
|
|
(only user). (Note that actually for a Unix domain socket, only write
|
|
permission matters and there is no point in setting or revoking
|
|
read or execute permissions.)
|
|
</para>
|
|
|
|
<para>
|
|
This access control mechanism is independent of the one
|
|
described in <xref linkend="client-authentication">.
|
|
</para>
|
|
|
|
<para>
|
|
This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>VACUUM_MEM</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the maximum amount of memory to be used by
|
|
<command>VACUUM</command> to keep track of to-be-reclaimed
|
|
tuples. The value is specified in kilobytes, and defaults to
|
|
8192 kilobytes. Larger settings may improve the speed of
|
|
vacuuming large tables that have many deleted tuples.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>VIRTUAL_HOST</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the host name or IP address on which the server is
|
|
to listen for connections from client applications. The
|
|
default is to listening on all configured addresses (including
|
|
<systemitem class="systemname">localhost</>).
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ZERO_DAMAGED_PAGES</varname> (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Detection of a damaged page header normally causes
|
|
<productname>PostgreSQL</> to report an error, aborting the current
|
|
transaction. Setting <varname>zero_damaged_pages</> to true causes
|
|
the system to instead report a warning, zero out the damaged page,
|
|
and continue processing. This behavior <emphasis>will destroy data</>,
|
|
namely all the rows on the damaged page. But it allows you to get
|
|
past the error and retrieve rows from any undamaged pages that may
|
|
be present in the table. So it is useful for recovering data if
|
|
corruption has occurred due to hardware or software error. You should
|
|
generally not set this true until you have given up hope of recovering
|
|
data from the damaged page(s) of a table. The
|
|
default setting is off, and it can only be changed by a superuser.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</sect2>
|
|
|
|
<sect2 id="runtime-config-wal">
|
|
<title>WAL</title>
|
|
|
|
<para>
|
|
See also <xref linkend="wal-configuration"> for details on WAL
|
|
tuning.
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><varname>CHECKPOINT_SEGMENTS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Maximum distance between automatic WAL checkpoints, in log file
|
|
segments (each segment is normally 16 megabytes).
|
|
This option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>CHECKPOINT_TIMEOUT</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Maximum time between automatic WAL checkpoints, in seconds.
|
|
This option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>CHECKPOINT_WARNING</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Send a message to the server logs if checkpoints caused by the
|
|
filling of checkpoint segment files happens more frequently than
|
|
this number of seconds. Zero turns off the warning.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>COMMIT_DELAY</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Time delay between writing a commit record to the WAL buffer and
|
|
flushing the buffer out to disk, in microseconds. A nonzero
|
|
delay allows multiple transactions to be committed with only one
|
|
<function>fsync</function> system call, if system load is high
|
|
enough additional transactions may become ready to commit within
|
|
the given interval. But the delay is just wasted if no other
|
|
transactions become ready to commit. Therefore, the delay is
|
|
only performed if at least <varname>COMMIT_SIBLINGS</varname> other transactions
|
|
are active at the instant that a server process has written its commit
|
|
record.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>COMMIT_SIBLINGS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Minimum number of concurrent open transactions to require before
|
|
performing the <varname>COMMIT_DELAY</> delay. A larger value
|
|
makes it more probable that at least one other transaction will
|
|
become ready to commit during the delay interval.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>WAL_BUFFERS</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Number of disk-page buffers in shared memory for WAL
|
|
logging. The default is 4. This option can only be set at
|
|
server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>WAL_DEBUG</varname> (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If nonzero, turn on WAL-related debugging output to the server log.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>WAL_SYNC_METHOD</varname> (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Method used for forcing WAL updates out to disk. Possible
|
|
values are
|
|
<literal>FSYNC</> (call <function>fsync()</> at each commit),
|
|
<literal>FDATASYNC</> (call <function>fdatasync()</> at each commit),
|
|
<literal>OPEN_SYNC</> (write WAL files with <function>open()</> option <symbol>O_SYNC</>), and
|
|
<literal>OPEN_DATASYNC</> (write WAL files with <function>open()</> option <symbol>O_DSYNC</>).
|
|
Not all of these choices are available on all platforms.
|
|
This option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="runtime-config-short">
|
|
<title>Short Options</title>
|
|
|
|
<para>
|
|
For convenience there are also single letter command-line option switches
|
|
available for some parameters. They are described in <xref
|
|
linkend="runtime-config-short-table">.
|
|
</para>
|
|
|
|
<table id="runtime-config-short-table">
|
|
<title>Short option key</title>
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row>
|
|
<entry>Short option</entry>
|
|
<entry>Equivalent</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><option>-B <replaceable>x</replaceable></option></entry>
|
|
<entry><literal>shared_buffers = <replaceable>x</replaceable></></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-d <replaceable>x</replaceable></option></entry>
|
|
<entry><literal>log_min_messages = DEBUG<replaceable>x</replaceable></></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-F</option></entry>
|
|
<entry><literal>fsync = off</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-h <replaceable>x</replaceable></option></entry>
|
|
<entry><literal>virtual_host = <replaceable>x</replaceable></></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-i</option></entry>
|
|
<entry><literal>tcpip_socket = on</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-k <replaceable>x</replaceable></option></entry>
|
|
<entry><literal>unix_socket_directory = <replaceable>x</replaceable></></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-l</option></entry>
|
|
<entry><literal>ssl = on</></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-N <replaceable>x</replaceable></option></entry>
|
|
<entry><literal>max_connections = <replaceable>x</replaceable></></entry>
|
|
</row>
|
|
<row>
|
|
<entry><option>-p <replaceable>x</replaceable></option></entry>
|
|
<entry><literal>port = <replaceable>x</replaceable></></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>
|
|
<option>-fi</option>, <option>-fh</option>,
|
|
<option>-fm</option>, <option>-fn</option>,
|
|
<option>-fs</option>, <option>-ft</option><footnote
|
|
id="fn.runtime-config-short">
|
|
<para>
|
|
For historical reasons, these options must be passed to
|
|
the individual server process via the <option>-o</option>
|
|
<command>postmaster</command> option, for example,
|
|
<screen>
|
|
$ <userinput>postmaster -o '-S 1024 -s'</userinput>
|
|
</screen>
|
|
or via <envar>PGOPTIONS</envar> from the client side, as
|
|
explained above.
|
|
</para>
|
|
</footnote>
|
|
</entry>
|
|
<entry>
|
|
<literal>enable_indexscan=off</>,
|
|
<literal>enable_hashjoin=off</>,
|
|
<literal>enable_mergejoin=off</>,
|
|
<literal>enable_nestloop=off</>,
|
|
<literal>enable_seqscan=off</>,
|
|
<literal>enable_tidscan=off</>
|
|
</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><option>-s</option><footnoteref linkend="fn.runtime-config-short"></entry>
|
|
<entry><literal>show_statement_stats = on</></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><option>-S <replaceable>x</replaceable></option><footnoteref linkend="fn.runtime-config-short">
|
|
</entry>
|
|
<entry><literal>sort_mem = <replaceable>x</replaceable></></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><option>-tpa</option>, <option>-tpl</option>, <option>-te</option><footnoteref linkend="fn.runtime-config-short"></entry>
|
|
<entry><literal>log_parser_stats=on</>,
|
|
<literal>log_planner_stats=on</>,
|
|
<literal>log_executor_stats=on</></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
</sect2>
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="kernel-resources">
|
|
<title>Managing Kernel Resources</title>
|
|
|
|
<para>
|
|
A large <productname>PostgreSQL</> installation can quickly exhaust
|
|
various operating system resource limits. (On some systems, the
|
|
factory defaults are so low that you don't even need a really
|
|
<quote>large</> installation.) If you have encountered this kind of
|
|
problem, keep reading.
|
|
</para>
|
|
|
|
<sect2 id="sysvipc">
|
|
<title>Shared Memory and Semaphores</title>
|
|
|
|
<indexterm zone="sysvipc">
|
|
<primary>shared memory</primary>
|
|
</indexterm>
|
|
|
|
<indexterm zone="sysvipc">
|
|
<primary>semaphores</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Shared memory and semaphores are collectively referred to as
|
|
<quote><systemitem class="osname">System V</>
|
|
<acronym>IPC</></quote> (together with message queues, which are not
|
|
relevant for <productname>PostgreSQL</>). Almost all modern
|
|
operating systems provide these features, but not all of them have
|
|
them turned on or sufficiently sized by default, especially systems
|
|
with BSD heritage. (For the <systemitem class="osname">QNX</> and
|
|
<systemitem class="osname">BeOS</> ports, <productname>PostgreSQL</>
|
|
provides its own replacement implementation of these facilities.)
|
|
</para>
|
|
|
|
<para>
|
|
The complete lack of these facilities is usually manifested by an
|
|
<errorname>Illegal system call</> error upon server start. In
|
|
that case there's nothing left to do but to reconfigure your
|
|
kernel. <productname>PostgreSQL</> won't work without them.
|
|
</para>
|
|
|
|
<para>
|
|
When <productname>PostgreSQL</> exceeds one of the various hard
|
|
<acronym>IPC</> limits, the server will refuse to start and
|
|
should leave an instructive error message describing the problem
|
|
encountered and what to do about it. (See also <xref
|
|
linkend="postmaster-start-failures">.) The relevant kernel
|
|
parameters are named consistently across different systems; <xref
|
|
linkend="sysvipc-parameters"> gives an overview. The methods to set
|
|
them, however, vary. Suggestions for some platforms are given below.
|
|
Be warned that it is often necessary to reboot your machine, and
|
|
possibly even recompile the kernel, to change these settings.
|
|
</para>
|
|
|
|
|
|
<table id="sysvipc-parameters">
|
|
<title><systemitem class="osname">System V</> <acronym>IPC</> parameters</>
|
|
|
|
<tgroup cols="3">
|
|
<thead>
|
|
<row>
|
|
<entry>Name</>
|
|
<entry>Description</>
|
|
<entry>Reasonable values</>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><varname>SHMMAX</></>
|
|
<entry>Maximum size of shared memory segment (bytes)</>
|
|
<entry>250 kB + 8.2 kB * <varname>shared_buffers</> + 14.2 kB * <varname>max_connections</> up to infinity</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SHMMIN</></>
|
|
<entry>Minimum size of shared memory segment (bytes)</>
|
|
<entry>1</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SHMALL</></>
|
|
<entry>Total amount of shared memory available (bytes or pages)</>
|
|
<entry>if bytes, same as <varname>SHMMAX</varname>; if pages, <literal>ceil(SHMMAX/PAGE_SIZE)</literal></>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SHMSEG</></>
|
|
<entry>Maximum number of shared memory segments per process</>
|
|
<entry>only 1 segment is needed, but the default is much higher</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SHMMNI</></>
|
|
<entry>Maximum number of shared memory segments system-wide</>
|
|
<entry>like <varname>SHMSEG</> plus room for other applications</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMMNI</></>
|
|
<entry>Maximum number of semaphore identifiers (i.e., sets)</>
|
|
<entry>at least <literal>ceil(max_connections / 16)</literal></>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMMNS</></>
|
|
<entry>Maximum number of semaphores system-wide</>
|
|
<entry><literal>ceil(max_connections / 16) * 17</literal> plus room for other applications</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMMSL</></>
|
|
<entry>Maximum number of semaphores per set</>
|
|
<entry>at least 17</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMMAP</></>
|
|
<entry>Number of entries in semaphore map</>
|
|
<entry>see text</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMVMX</></>
|
|
<entry>Maximum value of semaphore</>
|
|
<entry>at least 255 (The default is often 32767, don't change unless asked to.)</>
|
|
</row>
|
|
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
|
|
<para>
|
|
<indexterm><primary>SHMMAX</primary></indexterm> The most important
|
|
shared memory parameter is <varname>SHMMAX</>, the maximum size, in
|
|
bytes, of a shared memory segment. If you get an error message from
|
|
<function>shmget</> like <errorname>Invalid argument</>, it is
|
|
possible that this limit has been exceeded. The size of the required
|
|
shared memory segment varies both with the number of requested
|
|
buffers (<option>-B</> option) and the number of allowed connections
|
|
(<option>-N</> option), although the former is the most significant.
|
|
(You can, as a temporary solution, lower these settings to eliminate
|
|
the failure.) As a rough approximation, you can estimate the
|
|
required segment size by multiplying the number of buffers and the
|
|
block size (8 kB by default) plus ample overhead (at least half a
|
|
megabyte). Any error message you might get will contain the size of
|
|
the failed allocation request.
|
|
</para>
|
|
|
|
<para>
|
|
Less likely to cause problems is the minimum size for shared
|
|
memory segments (<varname>SHMMIN</>), which should be at most
|
|
approximately 256 kB for <productname>PostgreSQL</> (it is
|
|
usually just 1). The maximum number of segments system-wide
|
|
(<varname>SHMMNI</>) or per-process (<varname>SHMSEG</>) should
|
|
not cause a problem unless your system has them set to zero. Some
|
|
systems also have a limit on the total amount of shared memory in
|
|
the system; see the platform-specific instructions below.
|
|
</para>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</> uses one semaphore per allowed connection
|
|
(<option>-N</> option), in sets of 16. Each such set will also
|
|
contain a 17th semaphore which contains a <quote>magic
|
|
number</quote>, to detect collision with semaphore sets used by
|
|
other applications. The maximum number of semaphores in the system
|
|
is set by <varname>SEMMNS</>, which consequently must be at least
|
|
as high as the connection setting plus one extra for each 16
|
|
allowed connections (see the formula in <xref
|
|
linkend="sysvipc-parameters">). The parameter <varname>SEMMNI</>
|
|
determines the limit on the number of semaphore sets that can
|
|
exist on the system at one time. Hence this parameter must be at
|
|
least <literal>ceil(max_connections / 16)</>. Lowering the number
|
|
of allowed connections is a temporary workaround for failures,
|
|
which are usually confusingly worded <errorname>No space
|
|
left on device</>, from the function <function>semget</>.
|
|
</para>
|
|
|
|
<para>
|
|
In some cases it might also be necessary to increase
|
|
<varname>SEMMAP</> to be at least on the order of
|
|
<varname>SEMMNS</>. This parameter defines the size of the semaphore
|
|
resource map, in which each contiguous block of available semaphores
|
|
needs an entry. When a semaphore set is freed it is either added to
|
|
an existing entry that is adjacent to the freed block or it is
|
|
registered under a new map entry. If the map is full, the freed
|
|
semaphores get lost (until reboot). Fragmentation of the semaphore
|
|
space could over time lead to fewer available semaphores than there
|
|
should be.
|
|
</para>
|
|
|
|
<para>
|
|
The <varname>SEMMSL</> parameter, which determines how many
|
|
semaphores can be in a set, must be at least 17 for
|
|
<productname>PostgreSQL</>.
|
|
</para>
|
|
|
|
<para>
|
|
Various other settings related to <quote>semaphore undo</>, such as
|
|
<varname>SEMMNU</> and <varname>SEMUME</>, are not of concern
|
|
for <productname>PostgreSQL</>.
|
|
</para>
|
|
|
|
<variablelist>
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">BSD/OS</></term>
|
|
<indexterm><primary>BSD/OS</></>
|
|
<listitem>
|
|
<formalpara>
|
|
<title>Shared Memory</>
|
|
<para>
|
|
By default, only 4 MB of shared memory is supported. Keep in
|
|
mind that shared memory is not pageable; it is locked in RAM.
|
|
To increase the amount of shared memory supported by your
|
|
system, add the following to your kernel configuration
|
|
file. A <varname>SHMALL</> value of 1024 represents 4 MB of
|
|
shared memory. The following increases the maximum shared
|
|
memory area to 32 MB:
|
|
<programlisting>
|
|
options "SHMALL=8192"
|
|
options "SHMMAX=\(SHMALL*PAGE_SIZE\)"
|
|
</programlisting>
|
|
For those running 4.1 or later, just make the above changes,
|
|
recompile the kernel, and reboot.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<para>
|
|
For those running earlier releases, use <command>bpatch</> to
|
|
find the <varname>sysptsize</> value in the current
|
|
kernel. This is computed dynamically at boot time.
|
|
<screen>
|
|
$ <userinput>bpatch -r sysptsize</>
|
|
<computeroutput>0x9 = 9</>
|
|
</screen>
|
|
Next, add <varname>SYSPTSIZE</> as a hard-coded value in the
|
|
kernel configuration file. Increase the value you found using
|
|
<command>bpatch</>. Add 1 for every additional 4 MB of
|
|
shared memory you desire.
|
|
<programlisting>
|
|
options "SYSPTSIZE=16"
|
|
</programlisting>
|
|
<varname>sysptsize</> cannot be changed by <command>sysctl</command>.
|
|
</para>
|
|
|
|
<formalpara>
|
|
<title>Semaphores</>
|
|
<para>
|
|
You may need to increase the number of semaphores. By
|
|
default, <productname>PostgreSQL</> allocates 34 semaphores,
|
|
which is over half the default system total of 60. Set the
|
|
values you want in your kernel configuration file, e.g.:
|
|
<programlisting>
|
|
options "SEMMNI=40"
|
|
options "SEMMNS=240"
|
|
</programlisting>
|
|
</para>
|
|
</formalpara>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">FreeBSD</></term>
|
|
<term><systemitem class="osname">NetBSD</></term>
|
|
<term><systemitem class="osname">OpenBSD</></term>
|
|
<indexterm><primary>FreeBSD</></>
|
|
<indexterm><primary>NetBSD</></>
|
|
<indexterm><primary>OpenBSD</></>
|
|
<listitem>
|
|
<para>
|
|
The options <varname>SYSVSHM</> and <varname>SYSVSEM</> need
|
|
to be enabled when the kernel is compiled. (They are by
|
|
default.) The maximum size of shared memory is determined by
|
|
the option <varname>SHMMAXPGS</> (in pages). The following
|
|
shows an example of how to set the various parameters:
|
|
<programlisting>
|
|
options SYSVSHM
|
|
options SHMMAXPGS=4096
|
|
options SHMSEG=256
|
|
|
|
options SYSVSEM
|
|
options SEMMNI=256
|
|
options SEMMNS=512
|
|
options SEMMNU=256
|
|
options SEMMAP=256
|
|
</programlisting>
|
|
(On <systemitem class="osname">NetBSD</> and <systemitem
|
|
class="osname">OpenBSD</> the key word is actually
|
|
<literal>option</literal> singular.)
|
|
</para>
|
|
<para>
|
|
You might also want to use the <command>sysctl</> setting to
|
|
lock shared memory into RAM and prevent it from being paged out
|
|
to swap, e.g. <literal>kern.ipc.shm_use_phys</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">HP-UX</></term>
|
|
<indexterm><primary>HP-UX</></>
|
|
<listitem>
|
|
<para>
|
|
The default settings tend to suffice for normal installations.
|
|
On <productname>HP-UX</> 10, the factory default for
|
|
<varname>SEMMNS</> is 128, which might be too low for larger
|
|
database sites.
|
|
</para>
|
|
<para>
|
|
<acronym>IPC</> parameters can be set in the <application>System
|
|
Administration Manager</> (<acronym>SAM</>) under
|
|
<menuchoice><guimenu>Kernel
|
|
Configuration</><guimenuitem>Configurable Parameters</></>. Hit
|
|
<guibutton>Create A New Kernel</> when you're done.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">Linux</></term>
|
|
<indexterm><primary>Linux</></>
|
|
<listitem>
|
|
<para>
|
|
The default shared memory limit (both
|
|
<varname>SHMMAX</varname> and <varname>SHMALL</varname>) is 32
|
|
MB in 2.2 kernels, but it can be changed in the
|
|
<filename>proc</filename> file system (without reboot). For
|
|
example, to allow 128 MB:
|
|
<screen>
|
|
<prompt>$</prompt> <userinput>echo 134217728 >/proc/sys/kernel/shmall</userinput>
|
|
<prompt>$</prompt> <userinput>echo 134217728 >/proc/sys/kernel/shmmax</userinput>
|
|
</screen>
|
|
You could put these commands into a script run at boot-time.
|
|
</para>
|
|
|
|
<para>
|
|
Alternatively, you can use <command>sysctl</command>, if
|
|
available, to control these parameters. Look for a file
|
|
called <filename>/etc/sysctl.conf</filename> and add lines
|
|
like the following to it:
|
|
<programlisting>
|
|
kernel.shmall = 134217728
|
|
kernel.shmmax = 134217728
|
|
</programlisting>
|
|
This file is usually processed at boot time, but
|
|
<command>sysctl</command> can also be called
|
|
explicitly later.
|
|
</para>
|
|
|
|
<para>
|
|
Other parameters are sufficiently sized for any application. If
|
|
you want to see for yourself look in
|
|
<filename>/usr/src/linux/include/asm-<replaceable>xxx</>/shmpara
|
|
m.h</> and <filename>/usr/src/linux/include/linux/sem.h</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">MacOS X</></term>
|
|
<indexterm><primary>MacOS X</></>
|
|
<listitem>
|
|
<para>
|
|
Edit the file
|
|
<filename>/System/Library/StartupItems/SystemTuning/SystemTuning
|
|
</> and change the following values:
|
|
<programlisting>
|
|
sysctl -w kern.sysv.shmmax
|
|
sysctl -w kern.sysv.shmmin
|
|
sysctl -w kern.sysv.shmmni
|
|
sysctl -w kern.sysv.shmseg
|
|
sysctl -w kern.sysv.shmall
|
|
</programlisting>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">SCO OpenServer</></term>
|
|
<indexterm><primary>SCO OpenServer</></>
|
|
<listitem>
|
|
<para>
|
|
In the default configuration, only 512 kB of shared memory per
|
|
segment is allowed, which is about enough for <option>-B 24 -N
|
|
12</>. To increase the setting, first change to the directory
|
|
<filename>/etc/conf/cf.d</>. To display the current value of
|
|
<varname>SHMMAX</>, run
|
|
<programlisting>
|
|
./configure -y SHMMAX
|
|
</programlisting>
|
|
To set a new value for <varname>SHMMAX</>, run
|
|
<programlisting>
|
|
./configure SHMMAX=<replaceable>value</>
|
|
</programlisting>
|
|
where <replaceable>value</> is the new value you want to use
|
|
(in bytes). After setting <varname>SHMMAX</>, rebuild the kernel:
|
|
<programlisting>
|
|
./link_unix
|
|
</programlisting>
|
|
and reboot.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">Solaris</></term>
|
|
<indexterm><primary>Solaris</></>
|
|
<listitem>
|
|
<para>
|
|
At least in version 2.6, the default maximum size of a shared
|
|
memory segments is too low for <productname>PostgreSQL</>. The
|
|
relevant settings can be changed in <filename>/etc/system</>,
|
|
for example:
|
|
<programlisting>
|
|
set shmsys:shminfo_shmmax=0x2000000
|
|
set shmsys:shminfo_shmmin=1
|
|
set shmsys:shminfo_shmmni=256
|
|
set shmsys:shminfo_shmseg=256
|
|
|
|
set semsys:seminfo_semmap=256
|
|
set semsys:seminfo_semmni=512
|
|
set semsys:seminfo_semmns=512
|
|
set semsys:seminfo_semmsl=32
|
|
</programlisting>
|
|
You need to reboot for the changes to take effect.
|
|
</para>
|
|
|
|
<para>
|
|
See also <ulink
|
|
url="http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html"></>
|
|
for information on shared memory under
|
|
<productname>Solaris</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term><systemitem class="osname">UnixWare</></term>
|
|
<indexterm><primary>UnixWare</></>
|
|
<listitem>
|
|
<para>
|
|
On <productname>UnixWare</> 7, the maximum size for shared
|
|
memory segments is 512 kB in the default configuration. This
|
|
is enough for about <option>-B 24 -N 12</>. To display the
|
|
current value of <varname>SHMMAX</>, run
|
|
<programlisting>
|
|
/etc/conf/bin/idtune -g SHMMAX
|
|
</programlisting>
|
|
which displays the current, default, minimum, and maximum
|
|
values. To set a new value for <varname>SHMMAX</>,
|
|
run
|
|
<programlisting>
|
|
/etc/conf/bin/idtune SHMMAX <replaceable>value</>
|
|
</programlisting>
|
|
where <replaceable>value</> is the new value you want to use
|
|
(in bytes). After setting <varname>SHMMAX</>, rebuild the
|
|
kernel:
|
|
<programlisting>
|
|
/etc/conf/bin/idbuild -B
|
|
</programlisting>
|
|
and reboot.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
|
|
</sect2>
|
|
|
|
|
|
<sect2>
|
|
<title>Resource Limits</title>
|
|
|
|
<para>
|
|
Unix-like operating systems enforce various kinds of resource limits
|
|
that might interfere with the operation of your
|
|
<productname>PostgreSQL</productname> server. Of particular
|
|
importance are limits on the number of processes per user, the
|
|
number of open files per process, and the amount of memory available
|
|
to each process. Each of these have a <quote>hard</quote> and a
|
|
<quote>soft</quote> limit. The soft limit is what actually counts
|
|
but it can be changed by the user up to the hard limit. The hard
|
|
limit can only be changed by the root user. The system call
|
|
<function>setrlimit</function> is responsible for setting these
|
|
parameters. The shell's built-in command <command>ulimit</command>
|
|
(Bourne shells) or <command>limit</command> (<application>csh</>) is
|
|
used to control the resource limits from the command line. On
|
|
BSD-derived systems the file <filename>/etc/login.conf</filename>
|
|
controls the various resource limits set during login. See the
|
|
operating system documentation for details. The relevant
|
|
parameters are <varname>maxproc</varname>,
|
|
<varname>openfiles</varname>, and <varname>datasize</varname>. For
|
|
example:
|
|
<programlisting>
|
|
default:\
|
|
...
|
|
:datasize-cur=256M:\
|
|
:maxproc-cur=256:\
|
|
:openfiles-cur=256:\
|
|
...
|
|
</programlisting>
|
|
(<literal>-cur</literal> is the soft limit. Append
|
|
<literal>-max</literal> to set the hard limit.)
|
|
</para>
|
|
|
|
<para>
|
|
Kernels can also have system-wide limits on some resources.
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
On <productname>Linux</productname>
|
|
<filename>/proc/sys/fs/file-max</filename> determines the
|
|
maximum number of open files that the kernel will support. It can
|
|
be changed by writing a different number into the file or by
|
|
adding an assignment in <filename>/etc/sysctl.conf</filename>.
|
|
The maximum limit of files per process is fixed at the time the
|
|
kernel is compiled; see
|
|
<filename>/usr/src/linux/Documentation/proc.txt</filename> for
|
|
more information.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
The <productname>PostgreSQL</productname> server uses one process
|
|
per connection so you should provide for at least as many processes
|
|
as allowed connections, in addition to what you need for the rest
|
|
of your system. This is usually not a problem but if you run
|
|
several servers on one machine things might get tight.
|
|
</para>
|
|
|
|
<para>
|
|
The factory default limit on open files is often set to
|
|
<quote>socially friendly</quote> values that allow many users to
|
|
coexist on a machine without using an inappropriate fraction of
|
|
the system resources. If you run many servers on a machine this
|
|
is perhaps what you want, but on dedicated servers you may want to
|
|
raise this limit.
|
|
</para>
|
|
|
|
<para>
|
|
On the other side of the coin, some systems allow individual
|
|
processes to open large numbers of files; if more than a few
|
|
processes do so then the system-wide limit can easily be exceeded.
|
|
If you find this happening, and you do not want to alter the system-wide
|
|
limit, you can set <productname>PostgreSQL</productname>'s
|
|
<varname>max_files_per_process</varname> configuration parameter to
|
|
limit the consumption of open files.
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="postmaster-shutdown">
|
|
<title>Shutting Down the Server</title>
|
|
|
|
<para>
|
|
There are several ways to shut down the database server. You control
|
|
the type of shutdown by sending different signals to the server
|
|
process.
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><systemitem>SIGTERM</systemitem></term>
|
|
<listitem>
|
|
<para>
|
|
After receiving <systemitem>SIGTERM</systemitem>, the server
|
|
disallows new connections, but lets existing sessions end their
|
|
work normally. It shuts down only after all of the sessions
|
|
terminate normally. This is the <firstterm>Smart
|
|
Shutdown</firstterm>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><systemitem>SIGINT</systemitem></term>
|
|
<listitem>
|
|
<para>
|
|
The server disallows new connections and sends all existing
|
|
server processes <systemitem>SIGTERM</systemitem>, which will cause them
|
|
to abort their current transactions and exit promptly. It then
|
|
waits for the server processes to exit and finally shuts down. This is the
|
|
<firstterm>Fast Shutdown</firstterm>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><systemitem>SIGQUIT</systemitem></term>
|
|
<listitem>
|
|
<para>
|
|
This is the <firstterm>Immediate Shutdown</firstterm>, which
|
|
will cause the <command>postmaster</command> process to send a
|
|
<systemitem>SIGQUIT</systemitem> to all child processes and exit
|
|
immediately (without properly shutting itself down). The child processes
|
|
likewise exit immediately upon receiving
|
|
<systemitem>SIGQUIT</systemitem>. This will lead to recovery (by
|
|
replaying the WAL log) upon next start-up. This is recommended
|
|
only in emergencies.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
|
|
<important>
|
|
<para>
|
|
It is best not to use <systemitem>SIGKILL</systemitem> to shut down
|
|
the server. This will prevent the server from releasing
|
|
shared memory and semaphores, which may then have to be done by
|
|
manually.
|
|
</para>
|
|
</important>
|
|
|
|
<para>
|
|
The <acronym>PID</> of the <command>postmaster</command> process can be found using the
|
|
<command>ps</command> program, or from the file
|
|
<filename>postmaster.pid</filename> in the data directory. So for
|
|
example, to do a fast shutdown:
|
|
<screen>
|
|
$ <userinput>kill -INT `head -1 /usr/local/pgsql/data/postmaster.pid`</userinput>
|
|
</screen>
|
|
</para>
|
|
<para>
|
|
The program <command>pg_ctl</command> is a shell script
|
|
that provides a more convenient interface for shutting down the
|
|
server.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="ssl-tcp">
|
|
<title>Secure TCP/IP Connections with SSL</title>
|
|
|
|
<indexterm zone="ssl-tcp">
|
|
<primary>SSL</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</> has native support for using
|
|
<acronym>SSL</> connections to encrypt client/server communications
|
|
for increased security. This requires that
|
|
<productname>OpenSSL</productname> is installed on both client and
|
|
server systems and that support in <productname>PostgreSQL</> is
|
|
enabled at build time (see <xref linkend="installation">).
|
|
</para>
|
|
|
|
<para>
|
|
With <acronym>SSL</> support compiled in, the
|
|
<productname>PostgreSQL</> server can be started with
|
|
<acronym>SSL</> enabled by setting the parameter
|
|
<varname>ssl</varname> to on in <filename>postgresql.conf</>. When
|
|
starting in <acronym>SSL</> mode, the server will look for the
|
|
files <filename>server.key</> and <filename>server.crt</> in the
|
|
data directory, which should contain the server private key
|
|
and certificate, respectively. These files must be set up correctly
|
|
before an <acronym>SSL</>-enabled server can start. If the private key is
|
|
protected with a passphrase, the server will prompt for the
|
|
passphrase and will not start until it has been entered.
|
|
</para>
|
|
|
|
<para>
|
|
The server will listen for both standard and <acronym>SSL</>
|
|
connections on the same TCP port, and will negotiate with any
|
|
connecting client on whether to use <acronym>SSL</>. See <xref
|
|
linkend="client-authentication"> about how to force the server to
|
|
require use of <acronym>SSL</> for certain connections.
|
|
</para>
|
|
|
|
<para>
|
|
For details on how to create your server private key and certificate,
|
|
refer to the <productname>OpenSSL</> documentation. A simple
|
|
self-signed certificate can be used to get started for testing, but a
|
|
certificate signed by a certificate authority (<acronym>CA</>) (either one of the global
|
|
<acronym>CAs</> or a local one) should be used in production so the
|
|
client can verify the server's identity. To create a quick
|
|
self-signed certificate, use the following
|
|
<productname>OpenSSL</productname> command:
|
|
<programlisting>
|
|
openssl req -new -text -out server.req
|
|
</programlisting>
|
|
Fill out the information that <command>openssl</> asks for. Make sure
|
|
that you enter the local host name as <quote>Common Name</>; the challenge
|
|
password can be left blank. The programm will generate a key that is
|
|
passphrase protected; it will not accept a passphrase that is less
|
|
than four characters long. To remove the passphrase (as you must if
|
|
you want automatic start-up of the server), run the commands
|
|
<programlisting>
|
|
openssl rsa -in privkey.pem -out server.key
|
|
rm privkey.pem
|
|
</programlisting>
|
|
Enter the old passphrase to unlock the existing key. Now do
|
|
<programlisting>
|
|
openssl req -x509 -in server.req -text -key server.key -out server.crt
|
|
chmod og-rwx server.key
|
|
</programlisting>
|
|
to turn the certificate into a self-signed certificate and to copy the
|
|
key and certificate to where the server will look for them.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="ssh-tunnels">
|
|
<title>Secure TCP/IP Connections with <application>SSH</application> Tunnels</title>
|
|
|
|
<indexterm zone="ssh-tunnels">
|
|
<primary>ssh</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
One can use <application>SSH</application> to encrypt the network
|
|
connection between clients and a
|
|
<productname>PostgreSQL</productname> server. Done properly, this
|
|
provides an adequately secure network connection.
|
|
</para>
|
|
|
|
<para>
|
|
First make sure that an <application>SSH</application> server is
|
|
running properly on the same machine as the
|
|
<productname>PostgreSQL</productname> server and that you can log in using
|
|
<command>ssh</command> as some user. Then you can establish a secure
|
|
tunnel with a command like this from the client machine:
|
|
<programlisting>
|
|
ssh -L 3333:foo.com:5432 joe@foo.com
|
|
</programlisting>
|
|
The first number in the <option>-L</option> argument, 3333, is the
|
|
port number of your end of the tunnel; it can be chosen freely. The
|
|
second number, 5432, is the remote end of the tunnel: the port
|
|
number your server is using. The name or the address in between
|
|
the port numbers is the host with the database server you are going
|
|
to connect to. In order to connect to the database server using
|
|
this tunnel, you connect to port 3333 on the local machine:
|
|
<programlisting>
|
|
psql -h localhost -p 3333 template1
|
|
</programlisting>
|
|
To the database server it will then look as though you are really
|
|
user <literal>joe@foo.com</literal> and it will use whatever
|
|
authentication procedure was set up for this user. In order for the
|
|
tunnel setup to succeed you must be allowed to connect via
|
|
<command>ssh</command> as <literal>joe@foo.com</literal>, just
|
|
as if you had attempted to use <command>ssh</command> to set up a
|
|
terminal session.
|
|
</para>
|
|
|
|
<tip>
|
|
<para>
|
|
Several other applications exist that can provide secure tunnels using
|
|
a procedure similar in concept to the one just described.
|
|
</para>
|
|
</tip>
|
|
|
|
</sect1>
|
|
|
|
</Chapter>
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
Local variables:
|
|
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|
|
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|
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|
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|
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|
|
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|
|
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|
|
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|
|
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|
|
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|
|
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|
|
End:
|
|
-->
|