mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-08-22 05:53:22 +02:00
2230 lines
78 KiB
Plaintext
2230 lines
78 KiB
Plaintext
<!--
|
|
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.66 2001/05/12 22:51:35 petere Exp $
|
|
-->
|
|
|
|
<Chapter Id="runtime">
|
|
<Title>Server Runtime Environment</Title>
|
|
|
|
<Para>
|
|
This chapter discusses how to set up and run the database server
|
|
and the interactions with the operating system.
|
|
</para>
|
|
|
|
<sect1 id="postgres-user">
|
|
<title>The Postgres user account</title>
|
|
|
|
<indexterm>
|
|
<primary>postgres user</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
As with any other server daemon that is connected to the world at
|
|
large, it is advisable to run Postgres under a separate user
|
|
account. This user account should only own the data itself that is
|
|
being managed by the server, and should not be shared with other
|
|
daemons. (Thus, using the user <quote>nobody</quote> is a bad
|
|
idea.) It is not advisable to install the executables as owned by
|
|
this user account because that runs the risk of user-defined
|
|
functions gone astray or any other exploits compromising the
|
|
executable programs.
|
|
</para>
|
|
|
|
<para>
|
|
To add a user account to your system, look for a command
|
|
<command>useradd</command> or <command>adduser</command>. The user
|
|
name <quote>postgres</quote> is often used but by no means
|
|
required.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="creating-cluster">
|
|
<title>Creating a database cluster</title>
|
|
|
|
<indexterm>
|
|
<primary>database cluster</primary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>data area</primary>
|
|
<see>database cluster</see>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Before you can do anything, you must initialize a database storage
|
|
area on disk. We call this a <firstterm>database
|
|
cluster</firstterm>. (<acronym>SQL</acronym> speaks of a catalog
|
|
cluster instead.) A database cluster is a collection of databases
|
|
that will be accessible through a single instance of a running
|
|
database server. After initialization, a database cluster will
|
|
contain one database named <literal>template1</literal>. As the
|
|
name suggests, this will be used as a template for any subsequently
|
|
created database; it should not be used for actual work.
|
|
</para>
|
|
|
|
<para>
|
|
In file system terms, a database cluster will be a single directory
|
|
under which all data will be stored. We call this the
|
|
<firstterm>data directory</firstterm> or <firstterm>data
|
|
area</firstterm>. It is completely up to you where you choose to
|
|
store your data, there is no default, although locations such as
|
|
<filename>/usr/local/pgsql/data</filename> or
|
|
<filename>/var/lib/pgsql/data</filename> are popular. To initialize
|
|
a database cluster, use the command <command>initdb</command>,
|
|
which is installed with <productname>PostgreSQL</productname>. The
|
|
desired file system location of your database system is indicated
|
|
by the <option>-D</option> option, for example
|
|
<screen>
|
|
> <userinput>initdb -D /usr/local/pgsql/data</userinput>
|
|
</screen>
|
|
Note that you must execute this command while being logged in to
|
|
the Postgres user account, which is described in the previous
|
|
section.
|
|
</para>
|
|
|
|
<tip>
|
|
<para>
|
|
<indexterm>
|
|
<primary><envar>PGDATA</envar></primary>
|
|
</indexterm>
|
|
As an alternative to the <option>-D</option> option, you can set
|
|
the environment variable <envar>PGDATA</envar>.
|
|
</para>
|
|
</tip>
|
|
|
|
<para>
|
|
<command>initdb</command> will attempt to create the directory you
|
|
specify if it does not already exist. It is likely that it won't
|
|
have the permission to do so (if you followed our advice and
|
|
created an unprivileged account). In that case you should create the
|
|
directory yourself (as root) and transfer ownership of it to the
|
|
Postgres user account. Here is how this might work:
|
|
<screen>
|
|
root# <userinput>mkdir /usr/local/pgsql/data</userinput>
|
|
root# <userinput>chown postgres /usr/local/pgsql/data</userinput>
|
|
root# <userinput>su postgres</userinput>
|
|
postgres> <userinput>initdb -D /usr/local/pgsql/data</userinput>
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
<command>initdb</command> will refuse to run if the data directory
|
|
looks like it belongs to an already initialized installation.
|
|
</para>
|
|
|
|
<para>
|
|
Because the data directory contains all the data stored in the
|
|
database it is essential that it be well secured from unauthorized
|
|
access. <command>initdb</command> therefore revokes access
|
|
permissions from everyone but the Postgres user account.
|
|
</para>
|
|
|
|
<para>
|
|
One surprise you might encounter while running <command>initdb</command> is
|
|
a notice similar to this one:
|
|
<screen>
|
|
NOTICE: Initializing database with en_US collation order.
|
|
This locale setting will prevent use of index optimization for
|
|
LIKE and regexp searches. If you are concerned about speed of
|
|
such queries, you may wish to set LC_COLLATE to "C" and
|
|
re-initdb. For more information see the Administrator's Guide.
|
|
</screen>
|
|
This notice is intended to warn you that the currently selected locale
|
|
will cause indexes to be sorted in an order that prevents them from
|
|
being used for LIKE and regular-expression searches. If you need
|
|
good performance of such searches, you should set your current locale
|
|
to "C" and re-run <command>initdb</command>. On most systems, setting the
|
|
current locale is done by changing the value of the environment variable
|
|
<literal>LC_ALL</literal> or <literal>LANG</literal>. The sort order used
|
|
within a particular database cluster is set by <command>initdb</command>
|
|
and cannot be changed later, short of dumping all data, re-initdb,
|
|
reload data. So it's important to make this choice correctly now.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="postmaster-start">
|
|
<title>Starting the database server</title>
|
|
|
|
<para>
|
|
<indexterm>
|
|
<primary>postmaster</primary>
|
|
</indexterm>
|
|
Before anyone can access the database you must start the database
|
|
server. The database server is called
|
|
<firstterm>postmaster</firstterm>.
|
|
The postmaster must know where to find the data it is supposed
|
|
to work on. This is done with the <option>-D</option> option. Thus,
|
|
the simplest way to start the server is, for example,
|
|
<screen>
|
|
> <userinput>postmaster -D /usr/local/pgsql/data</userinput>
|
|
</screen>
|
|
which will leave the server running in the foreground. This must
|
|
again be done while logged in to the Postgres user account. Without
|
|
a <option>-D</option>, the server will try to use the data
|
|
directory in the environment variable <envar>PGDATA</envar>; if
|
|
neither of these works it will fail.
|
|
</para>
|
|
|
|
<para>
|
|
To start the <application>postmaster</application> in the
|
|
background, use the usual shell syntax:
|
|
<screen>
|
|
> <userinput>postmaster -D /usr/local/pgsql/data > logfile 2>&1 &</userinput>
|
|
</screen>
|
|
It is an extremely good idea to keep the server output around
|
|
somewhere, as indicated here. It will help both for auditing
|
|
purposes and to diagnose problems.
|
|
</para>
|
|
|
|
<para>
|
|
<indexterm>
|
|
<primary>TCP/IP</primary>
|
|
</indexterm>
|
|
The postmaster also takes a number of other command line options.
|
|
For more information see the reference page and below under runtime
|
|
configuration. In particular, in order for the postmaster to accept
|
|
TCP/IP connections (rather than just Unix domain socket ones), you
|
|
must also specify the <option>-i</option> option.
|
|
</para>
|
|
|
|
<para>
|
|
<indexterm>
|
|
<primary>pg_ctl</primary>
|
|
</indexterm>
|
|
This shell syntax can get tedious quickly. Therefore the shell
|
|
script wrapper <application>pg_ctl</application> is provided that
|
|
encapsulates some of the tasks. E.g.,
|
|
<programlisting>
|
|
pg_ctl start -l logfile
|
|
</programlisting>
|
|
will start the server in the background and put the output into the
|
|
named log file. The <option>-D</option> option has the same
|
|
meaning as when invoking postmaster directly.
|
|
<application>pg_ctl</application> also implements a symmetric
|
|
<quote>stop</quote> operation.
|
|
</para>
|
|
|
|
<para>
|
|
Normally, you will want to start the database server when the
|
|
computer boots up. This is not required; the
|
|
<productname>PostgreSQL</productname> server can be run
|
|
successfully from non-privileged accounts without root
|
|
intervention.
|
|
</para>
|
|
|
|
<para>
|
|
Different systems have different conventions for starting up
|
|
daemons at boot time, so you are advised to familiarize yourself
|
|
with them. Many systems have a file
|
|
<filename>/etc/rc.local</filename> or
|
|
<filename>/etc/rc.d/rc.local</filename> which is almost certainly
|
|
no bad place to put such a command. Whatever you do, the server
|
|
must be run by the <productname>Postgres</productname> user account
|
|
<emphasis>and not by root</emphasis> or any other user. Therefore
|
|
you probably always want to form your command lines along the lines
|
|
of <literal>su -c '...' postgres</literal>, for example:
|
|
<programlisting>
|
|
su -c 'pg_ctl -D /usr/local/pgsql/data -l serverlog' postgres
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Here are a few more operating system specific suggestions. (Always
|
|
replace the proper installation directory and the user name you
|
|
chose.)
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
For <productname>FreeBSD</productname>, take a look at the file
|
|
<filename>contrib/start-scripts/freebsd</filename> in the
|
|
<productname>PostgreSQL</productname> source distribution.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
On <productname>OpenBSD</productname>, add the following lines
|
|
to the file <filename>/etc/rc.local</filename>:
|
|
<programlisting>
|
|
if [ -x /usr/local/pgsql/bin/pg_ctl -a -x /usr/local/pgsql/bin/postmaster ]; then
|
|
su - -c '/usr/local/pgsql/bin/pg_ctl start -l /var/postgresql/log -s' postgres
|
|
echo -n ' postgresql'
|
|
fi
|
|
</programlisting>
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
On <productname>Linux</productname> systems either add
|
|
<programlisting>
|
|
/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data
|
|
</programlisting>
|
|
to <filename>/etc/rc.d/rc.local</filename> or look into the file
|
|
<filename>contrib/start-scripts/linux</filename> in the
|
|
<productname>PostgreSQL</productname> source distribution to
|
|
integrate the start and shutdown into the run level system.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
On <productname>NetBSD</productname>, either use the
|
|
<productname>FreeBSD</productname> or
|
|
<productname>Linux</productname> start scripts, depending on
|
|
preference, as an example and place the file at
|
|
<filename>/usr/local/etc/rc.d/postgresql</filename>.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
On <productname>Solaris</productname>, create a file called
|
|
<filename>/etc/init.d/postgresql</filename> to contain the following
|
|
single line:
|
|
<programlisting>
|
|
su - postgres -c "/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data"
|
|
</programlisting>
|
|
Then, create a symlink to it in <filename>/etc/rc3.d</> as
|
|
<literal>S99postgresql</>.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
</para>
|
|
|
|
<para>
|
|
While the <application>postmaster</application> is running, its
|
|
PID is in the file <filename>postmaster.pid</filename> in the data
|
|
directory. This is used as an interlock against multiple postmasters
|
|
running in the same data directory, and can also be used for
|
|
shutting down the postmaster.
|
|
</para>
|
|
|
|
<sect2 id="postmaster-start-failures">
|
|
<title>Server Start-up Failures</title>
|
|
|
|
<para>
|
|
There are several common reasons for the postmaster to fail to
|
|
start up. Check the postmaster's log file, or start it by hand
|
|
(without redirecting standard output or standard error) to see
|
|
what complaint messages appear. Some of the possible error
|
|
messages are reasonably self-explanatory, but here are some that
|
|
are not.
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
FATAL: StreamServerPort: bind() failed: Address already in use
|
|
Is another postmaster already running on that port?
|
|
</screen>
|
|
This usually means just what it suggests: you accidentally
|
|
started a second postmaster on the same port where one is already
|
|
running. However, if the kernel error message is not
|
|
<computeroutput>Address already in use</computeroutput> or some
|
|
variant of that wording, there may be a different problem. For
|
|
example, trying to start a postmaster on a reserved port number
|
|
may draw something like
|
|
<screen>
|
|
> <userinput>postmaster -i -p 666</userinput>
|
|
FATAL: StreamServerPort: bind() failed: Permission denied
|
|
Is another postmaster already running on that port?
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
A message like
|
|
<screen>
|
|
IpcMemoryCreate: shmget(key=5440001, size=83918612, 01600) failed: Invalid argument
|
|
FATAL 1: ShmemCreate: cannot create region
|
|
</screen>
|
|
probably means that your kernel's limit on the size of shared
|
|
memory areas is smaller than the buffer area that Postgres is
|
|
trying to create (83918612 bytes in this example). Or it could
|
|
mean that you don't have System-V-style shared memory support
|
|
configured into your kernel at all. As a temporary workaround,
|
|
you can try starting the postmaster with a smaller-than-normal
|
|
number of buffers (<option>-B</option> switch). You will
|
|
eventually want to reconfigure your kernel to increase the
|
|
allowed shared memory size, however. You may see this message
|
|
when trying to start multiple postmasters on the same machine, if
|
|
their total space requests exceed the kernel limit.
|
|
</para>
|
|
|
|
<para>
|
|
An error like
|
|
<screen>
|
|
IpcSemaphoreCreate: semget(key=5440026, num=16, 01600) failed: No space left on device
|
|
</screen>
|
|
does <emphasis>not</emphasis> mean that you've run out of disk
|
|
space; it means that your kernel's limit on the number of System
|
|
V semaphores is smaller than the number
|
|
<productname>Postgres</productname> wants to create. As above,
|
|
you may be able to work around the problem by starting the
|
|
postmaster with a reduced number of backend processes
|
|
(<option>-N</option> switch), but you'll eventually want to
|
|
increase the kernel limit.
|
|
</para>
|
|
|
|
<para>
|
|
If you get an <quote>illegal system call</> error, then it is likely that
|
|
shared memory or semaphores are not supported at all in your kernel. In
|
|
that case your only option is to re-configure the kernel to turn on these
|
|
features.
|
|
</para>
|
|
|
|
<para>
|
|
Details about configuring System V IPC facilities are given in
|
|
<xref linkend="sysvipc">.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="client-connection-problems">
|
|
<title>Client Connection Problems</title>
|
|
|
|
<para>
|
|
Although the possible error conditions on the client side are
|
|
both virtually infinite and application dependent, a few of them
|
|
might be directly related to how the server was started up.
|
|
Conditions other than those shown below should be documented with
|
|
the respective client application.
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
PQconnectPoll() -- connect() failed: Connection refused
|
|
Is the postmaster running (with -i) at 'server.joe.com'
|
|
and accepting connections on TCP/IP port 5432?
|
|
</screen>
|
|
This is the generic <quote>I couldn't find a server to talk
|
|
to</quote> failure. It looks like the above when TCP/IP
|
|
communication is attempted. A common mistake is to forget the
|
|
<option>-i</option> to the postmaster to allow TCP/IP
|
|
connections.
|
|
</para>
|
|
|
|
<para>
|
|
Alternatively, you'll get this when attempting
|
|
Unix-socket communication to a local postmaster:
|
|
<screen>
|
|
connectDBstart() -- connect() failed: No such file or directory
|
|
Is the postmaster running locally
|
|
and accepting connections on Unix socket '/tmp/.s.PGSQL.5432'?
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
The last line is useful in verifying that the client is trying to
|
|
connect where it is supposed to. If there is in fact no
|
|
postmaster running there, the kernel error message will typically
|
|
be either <computeroutput>Connection refused</computeroutput> or
|
|
<computeroutput>No such file or directory</computeroutput>, as
|
|
illustrated. (It is particularly important to realize that
|
|
<computeroutput>Connection refused</computeroutput> in this
|
|
context does <emphasis>not</emphasis> mean that the postmaster
|
|
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>
|
|
|
|
<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 in some way or other. Here we
|
|
describe how to set them and the following subsections will
|
|
discuss each of them.
|
|
</para>
|
|
|
|
<para>
|
|
All parameter names are case-insensitive. Every parameter takes a
|
|
value of one of the four types boolean, integer, floating point,
|
|
string as described below. Boolean values are
|
|
<literal>ON</literal>, <literal>OFF</literal>,
|
|
<literal>TRUE</literal>, <literal>FALSE</literal>,
|
|
<literal>YES</literal>, <literal>NO</literal>,
|
|
<literal>1</literal>, <literal>0</literal> (case-insensitive) or
|
|
any non-ambiguous prefix of these.
|
|
</para>
|
|
|
|
<para>
|
|
One way to set these options is to create a file
|
|
<filename>postgresql.conf</filename> in the data directory (e.g.,
|
|
<filename>/usr/local/pgsql/data</filename>). An example of what
|
|
this file could look like is:
|
|
<programlisting>
|
|
# This is a comment
|
|
log_connections = yes
|
|
syslog = 2
|
|
</programlisting>
|
|
As you see, options are one per line. The equal sign between name
|
|
and value is optional. White space is insignificant, blank lines
|
|
are ignored. Hash marks (<quote>#</quote>) introduce comments
|
|
anywhere.
|
|
</para>
|
|
|
|
<para>
|
|
<indexterm>
|
|
<primary>SIGHUP</primary>
|
|
</indexterm>
|
|
The configuration file is reread whenever the postmaster receives
|
|
a SIGHUP signal. This signal is also propagated to all running
|
|
backend processes, so that running sessions get the new default.
|
|
Alternatively, you can send the signal to only one backend process
|
|
directly.
|
|
</para>
|
|
|
|
<para>
|
|
A second way to set these configuration parameters is to give them
|
|
as a command line option to the postmaster, such as
|
|
<programlisting>
|
|
postmaster -c log_connections=yes -c syslog=2
|
|
</programlisting>
|
|
which would have the same effect as the previous example.
|
|
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 backend 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 client application, not just
|
|
<application>psql</application>.) Note that this won't work for
|
|
options that are necessarily fixed once the server is started,
|
|
such as the port number.
|
|
</para>
|
|
|
|
<para>
|
|
Finally, some options can be changed in individual SQL sessions
|
|
with the <command>SET</command> command, for example
|
|
<screen>
|
|
=> <userinput>SET ENABLE_SEQSCAN TO OFF;</userinput>
|
|
</screen>
|
|
See the SQL command language reference for details on the syntax.
|
|
</para>
|
|
|
|
<sect2 id="runtime-config-optimizer">
|
|
<title>Planner and Optimizer Tuning</title>
|
|
|
|
<para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>CPU_INDEX_TUPLE_COST (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the query optimizer'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>CPU_OPERATOR_COST (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the optimizer's estimate of the cost of processing each
|
|
operator in a WHERE clause. This is measured as a fraction of
|
|
the cost of a sequential page fetch.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>CPU_TUPLE_COST (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the query optimizer'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>EFFECTIVE_CACHE_SIZE (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the optimizer'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>Postgres</productname> data files). This is
|
|
measured in disk pages, which are normally 8kB apiece.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>ENABLE_HASHJOIN (<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 mostly useful to debug the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>index scan</primary>
|
|
</indexterm>
|
|
|
|
<term>ENABLE_INDEXSCAN (<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 mostly useful to debug the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>ENABLE_MERGEJOIN (<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 mostly useful to debug the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>ENABLE_NESTLOOP (<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 is any other method available.
|
|
The default is on. This is mostly useful to debug the query
|
|
planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>sequential scan</primary>
|
|
</indexterm>
|
|
|
|
<term>ENABLE_SEQSCAN (<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 is any other method available.
|
|
The default is on. This is mostly useful to debug the query
|
|
planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>ENABLE_SORT (<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 is any other method available. The default
|
|
is on. This is mostly useful to debug the query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>ENABLE_TIDSCAN (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables the query planner's use of TID scan plan
|
|
types. The default is on. This is mostly useful to debug the
|
|
query planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>genetic query optimization</primary>
|
|
</indexterm>
|
|
<indexterm>
|
|
<primary>GEQO</primary>
|
|
<see>genetic query optimization</see>
|
|
</indexterm>
|
|
|
|
<term>GEQO (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Enables or disables genetic query optimization, which is an
|
|
algorithm that attempts to do query planning without
|
|
exhaustive search. This is on by default. See also the various
|
|
other GEQO_ settings.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>GEQO_EFFORT (<type>integer</type>)</term>
|
|
<term>GEQO_GENERATIONS (<type>integer</type>)</term>
|
|
<term>GEQO_POOL_SIZE (<type>integer</type>)</term>
|
|
<term>GEQO_RANDOM_SEED (<type>integer</type>)</term>
|
|
<term>GEQO_SELECTION_BIAS (<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 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
|
|
Effort * Log2(PoolSize) 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
|
|
reproduceable results from the algorithm. If it is set to -1
|
|
then the algorithm behaves non-deterministically.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>GEQO_THRESHOLD (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Use genetic query optimization to plan queries with at least
|
|
this many FROM items involved. (Note that a JOIN construct
|
|
counts as only one FROM item.) The default is 11. For simpler
|
|
queries it is usually best to use the
|
|
deterministic, exhaustive planner.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>KSQO (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
The <firstterm>Key Set Query Optimizer</firstterm>
|
|
(<abbrev>KSQO</abbrev>) causes the query planner to convert
|
|
queries whose WHERE clause contains many OR'ed AND clauses
|
|
(such as <literal>WHERE (a=1 AND b=2) OR (a=2 AND b=3)
|
|
...</literal>) into a UNION query. This method can be faster
|
|
than the default implementation, but it doesn't necessarily
|
|
give exactly the same results, since UNION implicitly adds a
|
|
SELECT DISTINCT clause to eliminate identical output rows.
|
|
KSQO is commonly used when working with products like
|
|
<productname>Microsoft Access</productname>, which tend to
|
|
generate queries of this form.
|
|
</para>
|
|
|
|
<para>
|
|
The KSQO algorithm used to be absolutely essential for queries
|
|
with many OR'ed AND clauses, but in
|
|
<productname>Postgres</productname> 7.0 and later the standard
|
|
planner handles these queries fairly successfully. Hence the
|
|
default is OFF.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>RANDOM_PAGE_COST (<type>floating point</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the query optimizer'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.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
Unfortunately, there is no well-defined method of 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>
|
|
|
|
<para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>DEBUG_ASSERTIONS (<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 Postgres is built (see the configure option
|
|
<literal>--enable-cassert</literal>). Note that
|
|
<literal>DEBUG_ASSERTIONS</literal> defaults to ON if Postgres
|
|
has been built this way.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>DEBUG_LEVEL (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
The higher this value is set, the more
|
|
<quote>debugging</quote> output of various sorts is generated
|
|
in the server log during operation. This option is 0 by
|
|
default, which means no debugging output. Values up to about 4
|
|
currently make sense.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>DEBUG_PRINT_QUERY (<type>boolean</type>)</term>
|
|
<term>DEBUG_PRINT_PARSE (<type>boolean</type>)</term>
|
|
<term>DEBUG_PRINT_REWRITTEN (<type>boolean</type>)</term>
|
|
<term>DEBUG_PRINT_PLAN (<type>boolean</type>)</term>
|
|
<term>DEBUG_PRETTY_PRINT (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
These flags enable various debugging output to be sent to the
|
|
server log. For each executed query, prints either the query text,
|
|
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.
|
|
Setting <option>DEBUG_LEVEL</option> above zero implicitly turns
|
|
on some of these flags.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>HOSTNAME_LOOKUP (<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>LOG_CONNECTIONS (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Prints a line informing about each successful connection to
|
|
the server log. This is off by default, although it is
|
|
probably very useful. This option can only be set at server
|
|
start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>LOG_PID (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Prefixes each server log message with the process id of the
|
|
backend process. This is useful to sort out which messages
|
|
pertain to which connection. The default is off.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>LOG_TIMESTAMP (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Prefixes each server log message with a timestamp. The default
|
|
is off.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SHOW_QUERY_STATS (<type>boolean</type>)</term>
|
|
<term>SHOW_PARSER_STATS (<type>boolean</type>)</term>
|
|
<term>SHOW_PLANNER_STATS (<type>boolean</type>)</term>
|
|
<term>SHOW_EXECUTOR_STATS (<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>SHOW_SOURCE_PORT (<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>SYSLOG (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
<productname>Postgres</productname> allows the use of
|
|
<application>syslog</application> for logging. If this option
|
|
is set to 1, messages go both to syslog and the standard
|
|
output. A setting of 2 sends output only to syslog. (Some
|
|
messages will still go to the standard output/error.) The
|
|
default is 0, which means syslog is off. This option must be
|
|
set at server start.
|
|
</para>
|
|
<para>
|
|
To use syslog, the build of
|
|
<productname>Postgres</productname> must be configured with
|
|
the <option>--enable-syslog</option> option.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SYSLOG_FACILITY (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This option determines the <application>syslog</application>
|
|
<quote>facility</quote> to be used when syslog is enabled.
|
|
You may choose from LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4,
|
|
LOCAL5, LOCAL6, LOCAL7; the default is LOCAL0. See also the
|
|
documentation of your system's
|
|
<application>syslog</application>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SYSLOG_IDENT (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If logging to 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 <quote>postgres</quote>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>TRACE_NOTIFY (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Generates a great amount of debugging output for the
|
|
<command>LISTEN</command> and <command>NOTIFY</command>
|
|
commands.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="runtime-config-general">
|
|
<title>General operation</title>
|
|
|
|
<para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>deadlock</primary>
|
|
<secondary>timeout</secondary>
|
|
</indexterm>
|
|
|
|
<term>DEADLOCK_TIMEOUT (<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 or not.
|
|
The check for deadlock is relatively slow, so we don't want to
|
|
run it every time we wait for a lock. We (optimistically?)
|
|
assume that deadlocks are not common in production applications,
|
|
and just wait on the lock for awhile before starting to ask
|
|
questions about whether it can ever get unlocked.
|
|
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 the lock will be released before the waiter decides to
|
|
check for deadlock.
|
|
This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>fsync</primary>
|
|
</indexterm>
|
|
|
|
<term>FSYNC (<type>boolean</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If this option is on, the <productname>Postgres</> backend
|
|
will use the <function>fsync()</> system call in several
|
|
places to make sure that updates are physically written to
|
|
disk and do not hang around in the kernel buffer cache. This
|
|
increases the chance that a database installation will still
|
|
be usable after an operating system or hardware crash by a
|
|
large amount. (Crashes of the database server itself do
|
|
<emphasis>not</> affect this consideration.)
|
|
</para>
|
|
|
|
<para>
|
|
However, this operation slows down <productname>Postgres</>,
|
|
because at all those points it has
|
|
to block and wait for the operating system to flush the
|
|
buffers. Without <function>fsync</>, the operating system is
|
|
allowed to do its best in buffering, sorting, and delaying
|
|
writes, which can make for a considerable perfomance
|
|
increase. 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>
|
|
This option is the subject of an eternal debate in the
|
|
<productname>Postgres</> user and developer communities. Some
|
|
always leave it off, some turn it off only for bulk loads,
|
|
where there is a clear restart point if something goes wrong,
|
|
some leave it on just to be on the safe side. Because it is
|
|
the safe side, on is also the default. If you trust your
|
|
operating system, your hardware, and your utility company (or
|
|
better your UPS), you might want to disable fsync.
|
|
</para>
|
|
|
|
<para>
|
|
It should be noted that the performance penalty from doing
|
|
fsyncs is considerably less in <productname>Postgres</> version
|
|
7.1 than it was in prior releases. If you previously suppressed
|
|
fsyncs because of performance problems, 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>KRB_SERVER_KEYFILE (<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>
|
|
<term>MAX_CONNECTIONS (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Determines how many concurrent connections the database server
|
|
will allow. The default is 32. There is also a compiled-in
|
|
hard upper limit on this value, which is typically 1024
|
|
(both numbers can be altered when compiling the server). This
|
|
parameter can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>MAX_EXPR_DEPTH (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the maximum expression nesting depth that the parser will
|
|
accept. The default value is high enough for any normal query,
|
|
but you can raise it if you need to. (But if you raise it too
|
|
high, you run the risk of backend crashes due to stack
|
|
overflow.)
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>PORT (<type>integer</type>)</term>
|
|
<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>SHARED_BUFFERS (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Sets the number of shared memory buffers the database server
|
|
will use. The default is 64. Each buffer is typically 8192
|
|
bytes. This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SILENT_MODE (<type>bool</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Runs postmaster silently. If this option is set, postmaster
|
|
will automatically run in background and any controlling ttys
|
|
are disassociated, thus no messages are written to stdout or
|
|
stderr (same effect as postmaster's -S option). Unless some
|
|
logging system such as syslog is enabled, using this option is
|
|
discouraged since it makes it impossible to see error
|
|
messages.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SORT_MEM (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the amount of memory to be used by internal sorts
|
|
and hashes before resorting to temporary disk files. The value
|
|
is specified in kilobytes, and defaults to 512 kilobytes. Note
|
|
that for a complex query, several sorts and/or hashes might be
|
|
running in parallel, and each one will be allowed to use as
|
|
much memory as this value specifies before it starts to put
|
|
data into temporary files. And don't forget that each running
|
|
backend could be doing one or more sorts. So the total memory
|
|
space needed could be many times the value of SORT_MEM.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SQL_INHERITANCE (<type>bool</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
This controls the inheritance semantics, in particular whether
|
|
subtables are included into the consideration of various
|
|
commands by default. This was not the case in versions prior
|
|
to 7.1. If you need the old behaviour 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>
|
|
keyword to exclude subtables. See the SQL language reference
|
|
and the <citetitle>User's Guide</citetitle> for more
|
|
information about inheritance.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<indexterm>
|
|
<primary>SSL</primary>
|
|
</indexterm>
|
|
|
|
<term>SSL (<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>TCPIP_SOCKET (<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>UNIX_SOCKET_DIRECTORY (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the directory of the Unix-domain socket on which the
|
|
<application>postmaster</application> 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>UNIX_SOCKET_GROUP (<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
|
|
postmaster.) In combination with the option
|
|
<option>UNIX_SOCKET_PERMISSIONS</option> 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>UNIX_SOCKET_PERMISSIONS (<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 would be
|
|
<literal>0770</literal> (only user and group, see also under
|
|
<option>UNIX_SOCKET_GROUP</option>) and
|
|
<literal>0700</literal> (only user). (Note that actually for
|
|
a Unix 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 from the one
|
|
described in <xref linkend="client-authentication">.
|
|
</para>
|
|
|
|
<para>
|
|
This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>VIRTUAL_HOST (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Specifies the TCP/IP hostname or address on which the
|
|
<application>postmaster</application> is to listen for
|
|
connections from client applications. Defaults to
|
|
listening on all configured addresses (including localhost).
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="runtime-config-wal">
|
|
<title>WAL</title>
|
|
|
|
<para>
|
|
See also <xref linkend="wal-configuration"> for details on WAL
|
|
tuning.
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>CHECKPOINT_SEGMENTS (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Maximum distance between automatic WAL checkpoints, in logfile
|
|
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>CHECKPOINT_TIMEOUT (<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>COMMIT_DELAY (<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 fsync,
|
|
if system load is high enough that additional transactions become
|
|
ready to commit within the given interval. But the delay is just
|
|
wasted time if no other transactions become ready to commit.
|
|
Therefore, the delay is only performed if at least COMMIT_SIBLINGS
|
|
other transactions are active at the instant that a backend has
|
|
written its commit record.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>COMMIT_SIBLINGS (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Minimum number of concurrent open transactions to require before
|
|
performing the 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>WAL_BUFFERS (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Number of disk-page buffers in shared memory for WAL log.
|
|
This option can only be set at server start.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>WAL_DEBUG (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
If non-zero, turn on WAL-related debugging output on standard
|
|
error.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>WAL_FILES (<type>integer</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Number of log files that are created in advance at checkpoint
|
|
time. This option can only be set at server start or in the
|
|
<filename>postgresql.conf</filename> file.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>WAL_SYNC_METHOD (<type>string</type>)</term>
|
|
<listitem>
|
|
<para>
|
|
Method used for forcing WAL updates out to disk. Possible
|
|
values are
|
|
<literal>FSYNC</> (call fsync() at each commit),
|
|
<literal>FDATASYNC</> (call fdatasync() at each commit),
|
|
<literal>OPEN_SYNC</> (write WAL files with open() option O_SYNC), or
|
|
<literal>OPEN_DATASYNC</> (write WAL files with open() option 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 option switches
|
|
available for many parameters. They are described in the following
|
|
table.
|
|
|
|
<table>
|
|
<title>Short option key</title>
|
|
<tgroup cols="3">
|
|
<colspec colnum="3" align="center">
|
|
<thead>
|
|
<row>
|
|
<entry>Short option</entry>
|
|
<entry>Equivalent</entry>
|
|
<entry>Remark</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>-B <replaceable>x</replaceable></entry>
|
|
<entry>shared_buffers = <replaceable>x</replaceable></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-d <replaceable>x</replaceable></entry>
|
|
<entry>debug_level = <replaceable>x</replaceable></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-F</entry>
|
|
<entry>fsync = off</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-h <replaceable>x</replaceable></entry>
|
|
<entry>virtual_host = <replaceable>x</replaceable></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-i</entry>
|
|
<entry>tcpip_socket = on</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-k <replaceable>x</replaceable></entry>
|
|
<entry>unix_socket_directory = <replaceable>x</replaceable></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-l</entry>
|
|
<entry>ssl = on</entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-N <replaceable>x</replaceable></entry>
|
|
<entry>max_connections = <replaceable>x</replaceable></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>-p <replaceable>x</replaceable></entry>
|
|
<entry>port = <replaceable>x</replaceable></entry>
|
|
<entry></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>-fi, -fh, -fm, -fn, -fs, -ft</entry>
|
|
<entry>enable_indexscan=off, enable_hashjoin=off,
|
|
enable_mergejoin=off, enable_nestloop=off, enable_seqscan=off,
|
|
enable_tidscan=off</entry>
|
|
<entry>*</entry>
|
|
</row>
|
|
<row>
|
|
<entry>-S <replaceable>x</replaceable></entry>
|
|
<entry>sort_mem = <replaceable>x</replaceable></entry>
|
|
<entry>*</entry>
|
|
</row>
|
|
<row>
|
|
<entry>-s</entry>
|
|
<entry>show_query_stats = on</entry>
|
|
<entry>*</entry>
|
|
</row>
|
|
<row>
|
|
<entry>-tpa, -tpl, -te</entry>
|
|
<entry>show_parser_stats=on, show_planner_stats=on, show_executor_stats=on</entry>
|
|
<entry>*</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
For historical reasons, options marked <quote>*</quote> must be
|
|
passed to the individual backend process via the
|
|
<option>-o</option> postmaster 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>
|
|
|
|
</sect2>
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="kernel-resources">
|
|
<title>Managing Kernel Resources</title>
|
|
|
|
<para>
|
|
A large <productname>Postgres</> installation can quickly hit
|
|
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 then 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>System V IPC</> (together with message queues, which are
|
|
not relevant for <productname>Postgres</>). 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 QNX and BeOS ports,
|
|
<productname>Postgres</> 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 postmaster start. In
|
|
that case there's nothing left to do but to reconfigure your
|
|
kernel -- <productname>Postgres</> won't work without them.
|
|
</para>
|
|
|
|
<para>
|
|
When <productname>Postgres</> exceeds one of the various hard
|
|
limits of the IPC resources then the postmaster will refuse to
|
|
start up and should leave a marginally instructive error message
|
|
about which problem was encountered and what needs to be done
|
|
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 at least, possibly even recompile the kernel, to change these
|
|
settings.
|
|
</para>
|
|
|
|
|
|
<table id="sysvipc-parameters">
|
|
<title>System V 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 + 8.2kB * buffers + 14.2kB * max_connections or 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 SHMMAX; if pages, ceil(SHMMAX/PAGE_SIZE)</>
|
|
</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>>= ceil(max_connections / 16)</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMMNS</></>
|
|
<entry>Maximum number of semaphores system-wide</>
|
|
<entry>ceil(max_connections / 16) * 17 + room for other applications</>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><varname>SEMMSL</></>
|
|
<entry>Maximum number of semaphores per set</>
|
|
<entry>>= 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>>= 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, that a shared memory segment can have.
|
|
If you get an error message from <function>shmget</> along the
|
|
lines of <errorname>Invalid argument</> then it is possible that
|
|
this limit has been exceeded. The size of the required shared
|
|
memory segments 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 dominant item.
|
|
(You can therefore, as a temporary solution, lower these settings
|
|
to get rid of the failures.) As a rough approximation you can
|
|
estimate the required segment size as the number of buffers times
|
|
the block size (8192 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
|
|
somewhere around 256 kB for <productname>Postgres</> (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>Postgres</> 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 avoid 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 <quote><errorname>No space
|
|
left on device</></>, from the function <function>semget()</>.
|
|
</para>
|
|
|
|
<para>
|
|
In some cases it might also turn out to 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 therefore over time lead to less
|
|
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>Postgres</>.
|
|
</para>
|
|
|
|
<para>
|
|
Various other settings related to <quote>semaphore undo</>, such as
|
|
<varname>SEMMNU</> and <varname>SEMUME</>, are not of concern
|
|
for <productname>Postgres</>.
|
|
</para>
|
|
|
|
|
|
<para>
|
|
<variablelist>
|
|
|
|
<varlistentry>
|
|
<term>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 number of shared buffers supported by the
|
|
postmaster, add the following to your kernel config file. A
|
|
<varname>SHMALL</> value of 1024 represents 4MB of shared
|
|
memory. The following increases the maximum shared memory area
|
|
to 32 MB:
|
|
<programlisting>
|
|
options "SHMALL=8192"
|
|
options "SHMMAX=\(SHMALL*PAGE_SIZE\)"
|
|
</programlisting>
|
|
</para>
|
|
</formalpara>
|
|
|
|
<para>
|
|
For those running 4.1 or later, just make the above changes,
|
|
recompile the kernel, and reboot. For those running earlier
|
|
releases, use <application>bpatch</> to find the
|
|
<varname>sysptsize</> value in the current kernel. This is
|
|
computed dynamically at bootup.
|
|
<screen>
|
|
$ <userinput>bpatch -r sysptsize</>
|
|
<computeroutput>0x9 = 9</>
|
|
</screen>
|
|
Next, add <varname>SYSPTSIZE</> as a hard-coded value in the
|
|
kernel config file. Increase the value you found using
|
|
<application>bpatch</>. Add 1 for every additional 4 MB of
|
|
shared memory you desire.
|
|
<programlisting>
|
|
options "SYSPTSIZE=16"
|
|
</programlisting>
|
|
<varname>sysptsize</> can not be changed by sysctl.
|
|
</para>
|
|
|
|
<formalpara>
|
|
<title>Semaphores</>
|
|
<para>
|
|
You may need to increase the number of semaphores. By
|
|
default, <productname>Postgres</> allocates 34 semaphores,
|
|
which is over half the default system total of 60.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<para>
|
|
Set the values you want in your kernel config file, e.g.:
|
|
<programlisting>
|
|
options "SEMMNI=40"
|
|
options "SEMMNS=240"
|
|
options "SEMUME=40"
|
|
options "SEMMNU=120"
|
|
</programlisting>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term>FreeBSD</term>
|
|
<term>OpenBSD</term>
|
|
<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>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term>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>
|
|
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>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
|
|
<citerefentry><refentrytitle>sysctl</refentrytitle>
|
|
<manvolnum>8</manvolnum></citerefentry>, 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
|
|
<application>sysctl</application> can also be called
|
|
explicitly later.
|
|
</para>
|
|
|
|
<para>
|
|
Other parameters are sufficiently sized for any application.
|
|
If you want to see for yourself look into
|
|
<filename>/usr/src/linux/include/asm-<replaceable>xxx</>/shmparam.h</>
|
|
and <filename>/usr/src/linux/include/linux/sem.h</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term>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 the directory to
|
|
<filename>/etc/conf/cf.d</>. To display the current value of
|
|
<varname>SHMMAX</>, in bytes, 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>Solaris</>
|
|
<listitem>
|
|
<para>
|
|
At least in version 2.6, the maximum size of a shared memory
|
|
segment is set too low for <productname>Postgres</>. 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 to make the changes effective.
|
|
</para>
|
|
|
|
<para>
|
|
See also <ulink
|
|
url="http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html">http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html</>
|
|
for information on shared memory under
|
|
<productname>Solaris</>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
|
|
<varlistentry>
|
|
<term>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, in bytes. 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>
|
|
|
|
</para>
|
|
</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>Postgres</productname> server. Of importance are
|
|
especially the limits on the number of processes per user, the
|
|
number of open files per process, and the amount of memory
|
|
available to a 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> (csh) is used to control the resource
|
|
limits from the command line. On BSD-derived systems the file
|
|
<filename>/etc/login.conf</filename> controls what values the
|
|
various resource limits are set to upon login. See
|
|
<citerefentry><refentrytitle>login.conf</refentrytitle>
|
|
<manvolnum>5</manvolnum></citerefentry> 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 generally also have an implementation-dependent
|
|
system-wide limit on some resources.
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
On <productname>Linux</productname>
|
|
<filename>/proc/sys/fs/file-max</filename> determines the
|
|
maximum number of files that the kernel will allocate. 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>Postgres</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>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="postmaster-shutdown">
|
|
<title>Shutting down the server</title>
|
|
|
|
<para>
|
|
Depending on your needs, there are several ways to shut down the
|
|
database server when your work is done. The differentiation is
|
|
done by what signal you send to the server process.
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>SIGTERM</term>
|
|
<listitem>
|
|
<para>
|
|
After receiving SIGTERM, the postmaster disallows new
|
|
connections, but lets existing backends end their work normally.
|
|
It shuts down only after all of the backends terminate by client
|
|
request.
|
|
This is the <firstterm>Smart Shutdown</firstterm>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SIGINT</term>
|
|
<listitem>
|
|
<para>
|
|
The postmaster disallows new connections and sends all existing
|
|
backends SIGTERM, which will cause them to abort their current
|
|
transactions and exit promptly. It then waits for the backends to exit
|
|
and finally shuts down the data base.
|
|
This is the <firstterm>Fast Shutdown</firstterm>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SIGQUIT</term>
|
|
<listitem>
|
|
<para>
|
|
This is the <firstterm>Immediate Shutdown</firstterm> which
|
|
will cause the postmaster to send a SIGQUIT to all backends and
|
|
exit immediately (without properly shutting down the database
|
|
system). The backends likewise exit immediately upon receiving
|
|
SIGQUIT. This will lead to recovery (by replaying the WAL log)
|
|
upon next start-up. This is recommended only in emergencies.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<caution>
|
|
<para>
|
|
It is best not to use SIGKILL to shut down the postmaster. This
|
|
will prevent the postmaster from releasing shared memory and
|
|
semaphores, which you may then have to do by hand.
|
|
</para>
|
|
</caution>
|
|
|
|
The PID of the postmaster process can be found using the
|
|
<application>ps</application> 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 <application>pg_ctl</application> is a shell script
|
|
that provides a more convenient interface for shutting down the
|
|
postmaster.
|
|
</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 connections over
|
|
<acronym>SSL</> to encrypt
|
|
client/server communications for increased security. This requires
|
|
<productname>OpenSSL</productname> to be installed on both client
|
|
and server systems and support enabled at build-time (see <xref
|
|
linkend="installation">).
|
|
</para>
|
|
|
|
<para>
|
|
With SSL support compiled in, the <productname>PostgreSQL</> server
|
|
can be started with the argument <option>-l</> (ell) to enable
|
|
SSL connections. When starting in SSL mode, the postmaster will look
|
|
for the files <filename>server.key</> and <filename>server.crt</> in
|
|
the data directory. These files should contain the server private key
|
|
and certificate respectively. These files must be set up correctly
|
|
before an SSL-enabled server can start. If the private key is protected
|
|
with a passphrase, the postmaster will prompt for the passphrase and will
|
|
not start until it has been entered.
|
|
</para>
|
|
|
|
<para>
|
|
The postmaster will listen for both standard and SSL connections
|
|
on the same TCP/IP port, and will negotiate with any connecting
|
|
client whether or not to use SSL.
|
|
See <xref linkend="client-authentication">
|
|
about how to force on the server side the use of 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 CA (either one of the global CAs or a local one) should be used in
|
|
production so the client can verify the servers identity. To create
|
|
a quick self-signed certificate, use the following OpenSSL command:
|
|
<programlisting>
|
|
openssl req -new -text -out cert.req
|
|
</programlisting>
|
|
Fill out the information that openssl asks for. Make sure that you enter
|
|
the local host name as Common Name; the challenge password can be
|
|
left blank. The script will generate a key that is passphrase protected;
|
|
it will not accept a pass phrase that is less than four characters long.
|
|
To remove the passphrase (as you must if you want automatic start-up of
|
|
the postmaster), run the commands
|
|
<programlisting>
|
|
openssl rsa -in privkey.pem -out cert.pem
|
|
</programlisting>
|
|
Enter the old passphrase to unlock the existing key. Now do
|
|
<programlisting>
|
|
openssl req -x509 -in cert.req -text -key cert.pem -out cert.cert
|
|
cp cert.pem <replaceable>$PGDATA</replaceable>/server.key
|
|
cp cert.cert <replaceable>$PGDATA</replaceable>/server.crt
|
|
</programlisting>
|
|
to turn the certificate into a self-signed certificate and to copy the
|
|
key and certificate to where the postmaster will look for them.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="ssh-tunnels">
|
|
<title>Secure TCP/IP Connections with SSH tunnels</title>
|
|
|
|
<indexterm zone="ssh-tunnels">
|
|
<primary>ssh</primary>
|
|
</indexterm>
|
|
|
|
<note>
|
|
<title>Acknowledgement</title>
|
|
<para>
|
|
Idea taken from an email by Gene Selkov, Jr.
|
|
(<email>selkovjr@mcs.anl.gov</>) written on 1999-09-08 in response
|
|
to a question from Eric Marsden.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
One can use <productname>ssh</productname> to encrypt the network
|
|
connection between clients and a
|
|
<productname>Postgres</productname> server. Done properly, this
|
|
should lead to an adequately secure network connection.
|
|
</para>
|
|
|
|
<para>
|
|
First make sure that an <productname>ssh</productname> server is
|
|
running properly on the same machine as
|
|
<productname>Postgres</productname> and that you can log in using
|
|
ssh as some user. Then you can establish a secure tunnel with a
|
|
command like this from the client machine:
|
|
<programlisting>
|
|
> <userinput>ssh -L 3333:foo.com:5432 joe@foo.com</userinput>
|
|
</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 backend 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 ssh as
|
|
joe@foo.com, just as if you had attempted to use ssh to set up a
|
|
terminal session.
|
|
</para>
|
|
|
|
<tip>
|
|
<para>
|
|
Several other products 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:
|
|
mode:sgml
|
|
sgml-omittag:nil
|
|
sgml-shorttag:t
|
|
sgml-minimize-attributes:nil
|
|
sgml-always-quote-attributes:t
|
|
sgml-indent-step:1
|
|
sgml-indent-data:t
|
|
sgml-parent-document:nil
|
|
sgml-default-dtd-file:"./reference.ced"
|
|
sgml-exposed-tags:nil
|
|
sgml-local-catalogs:("/usr/lib/sgml/catalog")
|
|
sgml-local-ecat-files:nil
|
|
End:
|
|
-->
|