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doc: improve configuration management section 

Patch by David Johnston

Backpatch through 9.4
This commit is contained in:
Bruce Momjian 2014-09-10 20:50:15 -04:00
parent acc8e41681
commit 4c4654afeb
1 changed files with 245 additions and 131 deletions
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doc/src/sgml/config.sgml
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@ -10,8 +10,8 @@
<para>
There are many configuration parameters that affect the behavior of
the database system. In the first section of this chapter, we
describe how to set configuration parameters. The subsequent sections
the database system. In the first section of this chapter we
describe how to interact with configuration parameters. The subsequent sections
discuss each parameter in detail.
</para>
@ -23,47 +23,100 @@
<para>
All parameter names are case-insensitive. Every parameter takes a
value of one of five types: Boolean, integer, floating point,
string or enum. Boolean values can be written as <literal>on</literal>,
<literal>off</literal>, <literal>true</literal>,
<literal>false</literal>, <literal>yes</literal>,
<literal>no</literal>, <literal>1</literal>, <literal>0</literal>
(all case-insensitive) or any unambiguous prefix of these.
value of one of five types: boolean, integer, floating point,
string, or enum.
</para>
<para>
Some settings specify a memory or time value. Each of these has an
implicit unit, which is either kilobytes, blocks (typically eight
kilobytes), milliseconds, seconds, or minutes. Default units can be
found by referencing <structname>pg_settings</>.<structfield>unit</>.
For convenience,
a different unit can also be specified explicitly. Valid memory units
are <literal>kB</literal> (kilobytes), <literal>MB</literal>
(megabytes), <literal>GB</literal> (gigabytes), and <literal>TB</literal> (terabytes); valid time units
are <literal>ms</literal> (milliseconds), <literal>s</literal>
(seconds), <literal>min</literal> (minutes), <literal>h</literal>
(hours), and <literal>d</literal> (days). Note that the multiplier
for memory units is 1024, not 1000.
</para>
<itemizedlist>
<para>
Parameters of type <quote>enum</> are specified in the same way as string
parameters, but are restricted to a limited set of values. The allowed
values can be found
from <structname>pg_settings</>.<structfield>enumvals</>.
Enum parameter values are case-insensitive.
</para>
<listitem>
<para>
<emphasis>Boolean:</emphasis> Values can be written as
<literal>on</literal>,
<literal>off</literal>,
<literal>true</literal>,
<literal>false</literal>,
<literal>yes</literal>,
<literal>no</literal>,
<literal>1</literal>,
<literal>0</literal>
(all case-insensitive) or any unambiguous prefix of these.
</para>
</listitem>
<listitem>
<para>
<emphasis>String:</emphasis> Enclose the value in
single-quotes. Values are case-insensitive. If multiple values
are allowed, separate them with commas.
</para>
</listitem>
<listitem>
<para>
<emphasis>Numeric (integer and floating point):</emphasis> Do
not use single-quotes (unless otherwise required) or thousand
separators.
</para>
</listitem>
<listitem>
<para>
<emphasis>Numeric or String with Unit (Memory &amp;
Time):</emphasis> These have an implicit unit, which is
either kilobytes, blocks (typically eight kilobytes),
milliseconds, seconds, or minutes. A unadorned numeric
value will use the default, which can be found by referencing
<structname>pg_settings</>.<structfield>unit</>. For convenience,
a different unit can also be specified explicitly via a string
value. It is case-sensitive and may include whitespace between
the value and the unit.
<itemizedlist>
<listitem>
<para>
Valid memory units are <literal>kB</literal> (kilobytes),
<literal>MB</literal> (megabytes), <literal>GB</literal>
(gigabytes), and <literal>TB</literal> (terabytes).
The multiplier for memory units is 1024, not 1000.
</para>
</listitem>
<listitem>
<para>
Valid time units are <literal>ms</literal> (milliseconds),
<literal>s</literal> (seconds), <literal>min</literal> (minutes),
<literal>h</literal> (hours), and <literal>d</literal> (days).
</para>
</listitem>
</itemizedlist>
</para>
</listitem>
<listitem>
<para>
<emphasis><quote>enum</>:</emphasis> These are specified
in the same way as string parameters, but are restricted
to a limited set of values that can be queried from
<structname>pg_settings</>.<structfield>enumvals</>:
<programlisting>
SELECT name, setting, enumvals FROM pg_settings WHERE enumvals IS NOT NULL;
</programlisting>
Enum parameter values are case-insensitive.
</para>
</listitem>
</itemizedlist>
</sect2>
<sect2 id="config-setting-configuration-file">
<title>Setting Parameters via the Configuration File</title>
<title>Parameter Interaction via Configuration File</title>
<para>
One way to set these parameters is to edit the file
The primary way to set these parameters is to edit the file
<filename>postgresql.conf</><indexterm><primary>postgresql.conf</></>,
which is normally kept in the data directory. (A default copy is
installed there when the database cluster directory is
initialized.) An example of what this file might look like is:
installed when the database cluster directory is initialized.)
An example of what this file might look like is:
<programlisting>
# This is a comment
log_connections = yes
@ -73,125 +126,186 @@ shared_buffers = 128MB
</programlisting>
One parameter is specified per line. The equal sign between name and
value is optional. Whitespace is insignificant and blank lines are
ignored. Hash marks (<literal>#</literal>) designate the remainder of the
line as a comment. Parameter values that are not simple identifiers or
numbers must be single-quoted. To embed a single quote in a parameter
value, write either two quotes (preferred) or backslash-quote.
ignored. Hash marks (<literal>#</literal>) designate the remainder
of the line as a comment. Parameter values that are not simple
identifiers or numbers must be single-quoted. To embed a single
quote in a parameter value write either two quotes (preferred)
or backslash-quote.
</para>
<para>
Parameters set in this way provide default values for the cluster.
The setting seen by active sessions will be this value unless
it is overridden. The following sections describe ways in which the
administrator or user can override these defaults.
</para>
<para>
<indexterm>
<primary>SIGHUP</primary>
<primary>SIGHUP</primary>
</indexterm>
The configuration file is reread whenever the main server process
receives a <systemitem>SIGHUP</> signal; this is most easily done by
running <literal>pg_ctl reload</> from the command-line or by calling
the SQL function <function>pg_reload_conf()</function>. The main
server process
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. Some parameters can only be set at server start;
any changes to their entries in the configuration file will be ignored
until the server is restarted. Invalid parameter settings in the
configuration file are likewise ignored (but logged) during
<systemitem>SIGHUP</> processing.
server process also propagates this signal to all currently running
server processes so that existing sessions also get the new value
when they complete their transactions. Alternatively, you can
send the signal to a single server process directly. Some parameters
can only be set at server start; any changes to their entries in the
configuration file will be ignored until the server is restarted.
Invalid parameter settings in the configuration file are likewise
ignored (but logged) during <systemitem>SIGHUP</> processing.
</para>
</sect2>
<sect2 id="config-setting-other-methods">
<title>Other Ways to Set Parameters</title>
<sect2 id="config-setting-sql-command-interaction">
<title>Parameter Interaction via SQL</title>
<para>
<productname>PostgreSQL</productname> provides three SQL
commands to establish configuration defaults that override those
configured globally. The evaluation of these defaults occurs
at the beginning of a new session, upon the user issuing <xref
linkend="SQL-DISCARD">, or if the server forces the session to
reload its configuration after a <systemitem>SIGHUP</systemitem>
signal.
</para>
<itemizedlist>
<listitem>
<para>
The <xref linkend="SQL-ALTERSYSTEM"> command provides an
SQL-accessible means of changing global defaults.
</para>
</listitem>
<listitem>
<para>
The <xref linkend="sql-alterdatabase"> command allows database
administrators to override global settings on a per-database basis.
</para>
</listitem>
<listitem>
<para>
The <xref linkend="sql-alterrole"> command allows database
administrators to override both global and per-database settings
with user-specific values.
</para>
</listitem>
</itemizedlist>
<para>
Once a client connects to the database PostgreSQL provides
two additional SQL commands to interact with session-local
configuration settings. Both of these commands have equivalent
system administration functions.
</para>
<itemizedlist>
<listitem>
<para>
The <xref linkend="SQL-SHOW"> command allows inspection of the
current value of all parameters. The corresponding function is
<function>current_setting(setting_name text)</function>.
</para>
</listitem>
<listitem>
<para>
The <xref linkend="SQL-SET"> command allows modification of the
current value of some parameters. The corresponding function is
<function>set_config(setting_name, new_value, is_local)</function>.
</para>
</listitem>
</itemizedlist>
<para>
A second way to set these configuration parameters is to give them
as a command-line option to the <command>postgres</command> command,
such as:
Both <command>SELECT</> and <command>UPDATE</>
can be issued against the system view <link
linkend="view-pg-settings"><structname>pg_settings</></> to view
and change session-local values.
</para>
<itemizedlist>
<listitem>
<para>
Querying this view is the same as <command>SHOW</> but provides
more detail, as well as allowing for joins against other relations
and the specification of filter criteria.
</para>
</listitem>
<listitem>
<para>
Using <xref linkend="SQL-UPDATE"> on this relation, specifically
updating the <structname>setting</> column, is the equivalent
of issuing SQL <command>SET</>, though all values must be
single-quoted. Note that the equivalent of
<programlisting>
SET configuration_parameter TO DEFAULT;
</>
is:
<programlisting>
UPDATE pg_settings SET setting = reset_val WHERE name = 'configuration_parameter';
</programlisting>
</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>Parameter Interaction via Shell</title>
<para>
In addition to setting global defaults or attaching
overrides at the database or role level, you can pass settings to
<productname>PostgreSQL</productname> via shell facilities.
Both the server and <application>libpq</> client library
accept parameter values via the shell.
</para>
<itemizedlist>
<listitem>
<para>
On the <emphasis>server</emphasis>, command-line options can be
passed to the <command>postgres</command> command directly via the
<option>-c</> parameter.
<programlisting>
postgres -c log_connections=yes -c log_destination='syslog'
</programlisting>
Command-line options override any conflicting settings in
<filename>postgresql.conf</filename>. Note that this means you won't
be able to change the value on-the-fly by editing
<filename>postgresql.conf</filename>, so while the command-line
method might be convenient, it can cost you flexibility later.
</para>
Settings provided this way override those resolved globally (via
<filename>postgresql.conf</> or <command>ALTER SYSTEM</>) but
are otherwise treated as being global for the purpose of database
and role overrides.
</para>
</listitem>
<para>
Occasionally it is 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:
<listitem>
<para>
On the <emphasis>libpq-client</emphasis>, command-line options can be
specified using the <envar>PGOPTIONS</envar> environment variable.
When connecting to the server, the contents of this variable are
sent to the server as if they were being executed via SQL <xref
linkend="SQL-SET"> at the beginning of the session.
</para>
<para>
However, the format of <envar>PGOPTIONS</envar> is similar to that
used when launching the <command>postgres</command> command.
Specifically, the <option>-c</> flag must be specified.
<programlisting>
env PGOPTIONS='-c geqo=off' psql
env PGOPTIONS="-c geqo=off -c statement_timeout='5 min'" psql
</programlisting>
(This works for any <application>libpq</>-based client application, not
just <application>psql</application>.) Note that this won't work for
parameters that are fixed when the server is started or that must be
specified in <filename>postgresql.conf</filename>.
</para>
</para>
<para>
Furthermore, it is possible to assign a set of parameter 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 <xref linkend="sql-alterrole">
and <xref linkend="sql-alterdatabase">,
respectively, are used to configure these settings. Per-database
settings override anything received from the
<command>postgres</command> command-line or the configuration
file, and in turn are overridden by per-user settings; both are
overridden by per-session settings.
</para>
<para>
Some parameters can be changed in individual <acronym>SQL</acronym>
sessions with the <xref linkend="SQL-SET">
command, for example:
<screen>
SET ENABLE_SEQSCAN TO OFF;
</screen>
If <command>SET</> is allowed, it overrides all other sources of
values for the parameter. Some parameters cannot be changed via
<command>SET</command>: for example, if they control behavior that
cannot be changed without restarting the entire
<productname>PostgreSQL</productname> server. Also, some parameters
require superuser permission to change via <command>SET</command> or
<command>ALTER</>.
</para>
<para>
Another way to change configuration parameters persistently is by
use of <xref linkend="SQL-ALTERSYSTEM">
command, for example:
<screen>
ALTER SYSTEM SET checkpoint_timeout TO 600;
</screen>
This command will allow users to change values persistently
through SQL command. The values will be effective after reload of server configuration
(<acronym>SIGHUP</>) or server startup. The effect of this command is similar to when
user manually changes values in <filename>postgresql.conf</filename>.
</para>
</sect2>
<sect2 id="config-setting-examining">
<title>Examining Parameter Settings</title>
<para>
The <xref linkend="SQL-SHOW">
command allows inspection of the current values of all parameters.
</para>
<para>
The virtual table <structname>pg_settings</structname> also allows
displaying and updating session run-time parameters; see <xref
linkend="view-pg-settings"> for details and a description of the
different variable types and when they can be changed.
<structname>pg_settings</structname> is equivalent to <command>SHOW</>
and <command>SET</>, but can be more convenient
to use because it can be joined with other tables, or selected from using
any desired selection condition. It also contains more information about
each parameter than is available from <command>SHOW</>.
</para>
<para>
Other clients and libraries might provide their own mechanisms,
via the shell or otherwise, that allow the user to alter session
settings without requiring the user to issue SQL commands.
</para>
</listitem>
</itemizedlist>
</sect2>