<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>
<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 &
+ 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
</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>
- <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:
-<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>
+ <itemizedlist>
+ <listitem>
+ <para>
+ The <xref linkend="SQL-ALTERSYSTEM"> command provides an
+ SQL-accessible means of changing global defaults.
+ </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:
-<programlisting>
-env PGOPTIONS='-c geqo=off' psql
-</programlisting>
- (This works for any <application>libpq</>-based client application, not
- just <application>psql</application>.) Note that this won't work for
- parameters that are fixed when the server is started or that must be
- specified in <filename>postgresql.conf</filename>.
- </para>
+ <listitem>
+ <para>
+ The <xref linkend="sql-alterdatabase"> command allows database
+ administrators to override global settings on a per-database basis.
+ </para>
+ </listitem>
- <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.
+ <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>
- 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</>.
+ 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>
- <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>.
+ <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 id="config-setting-examining">
- <title>Examining Parameter Settings</title>
+ <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>
- <para>
- The <xref linkend="SQL-SHOW">
- command allows inspection of the current values of all parameters.
- </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>
+ 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>
- 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>
+ <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 -c statement_timeout='5 min'" psql
+</programlisting>
+ </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>
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