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><H1
CLASS="SECT1"
><A
NAME="CONFIG-SETTING"
>18.1. Setting Parameters</A
></H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CONFIG-SETTING-NAMES-VALUES"
>18.1.1. Parameter Names and Values</A
></H2
><P
> 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 <TT
CLASS="LITERAL"
>on</TT
>,
<TT
CLASS="LITERAL"
>off</TT
>, <TT
CLASS="LITERAL"
>true</TT
>,
<TT
CLASS="LITERAL"
>false</TT
>, <TT
CLASS="LITERAL"
>yes</TT
>,
<TT
CLASS="LITERAL"
>no</TT
>, <TT
CLASS="LITERAL"
>1</TT
>, <TT
CLASS="LITERAL"
>0</TT
>
(all case-insensitive) or any unambiguous prefix of these.
</P
><P
> 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 <TT
CLASS="STRUCTNAME"
>pg_settings</TT
>.<TT
CLASS="STRUCTFIELD"
>unit</TT
>.
For convenience,
a different unit can also be specified explicitly. Valid memory units
are <TT
CLASS="LITERAL"
>kB</TT
> (kilobytes), <TT
CLASS="LITERAL"
>MB</TT
>
(megabytes), and <TT
CLASS="LITERAL"
>GB</TT
> (gigabytes); valid time units
are <TT
CLASS="LITERAL"
>ms</TT
> (milliseconds), <TT
CLASS="LITERAL"
>s</TT
>
(seconds), <TT
CLASS="LITERAL"
>min</TT
> (minutes), <TT
CLASS="LITERAL"
>h</TT
>
(hours), and <TT
CLASS="LITERAL"
>d</TT
> (days). Note that the multiplier
for memory units is 1024, not 1000.
</P
><P
> Parameters of type <SPAN
CLASS="QUOTE"
>"enum"</SPAN
> 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 <TT
CLASS="STRUCTNAME"
>pg_settings</TT
>.<TT
CLASS="STRUCTFIELD"
>enumvals</TT
>.
Enum parameter values are case-insensitive.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CONFIG-SETTING-CONFIGURATION-FILE"
>18.1.2. Setting Parameters via the Configuration File</A
></H2
><P
> One way to set these parameters is to edit the file
<TT
CLASS="FILENAME"
>postgresql.conf</TT
>,
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:
</P><PRE
CLASS="PROGRAMLISTING"
># This is a comment
log_connections = yes
log_destination = 'syslog'
search_path = '"$user", public'
shared_buffers = 128MB</PRE
><P>
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 (<TT
CLASS="LITERAL"
>#</TT
>) 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.
</P
><P
>
In addition to parameter settings, the <TT
CLASS="FILENAME"
>postgresql.conf</TT
>
file can contain <I
CLASS="FIRSTTERM"
>include directives</I
>, which specify
another file to read and process as if it were inserted into the
configuration file at this point. This feature allows a configuration
file to be divided into physically separate parts.
Include directives simply look like:
</P><PRE
CLASS="PROGRAMLISTING"
>include 'filename'</PRE
><P>
If the file name is not an absolute path, it is taken as relative to
the directory containing the referencing configuration file.
Inclusions can be nested.
</P
><P
>
There is also an <TT
CLASS="LITERAL"
>include_if_exists</TT
> directive, which acts
the same as the <TT
CLASS="LITERAL"
>include</TT
> directive, except for the behavior
when the referenced file does not exist or cannot be read. A regular
<TT
CLASS="LITERAL"
>include</TT
> will consider this an error condition, but
<TT
CLASS="LITERAL"
>include_if_exists</TT
> merely logs a message and continues
processing the referencing configuration file.
</P
><P
>
The configuration file is reread whenever the main server process
receives a
<SPAN
CLASS="SYSTEMITEM"
>SIGHUP</SPAN
> signal (which is most easily sent by means
of <TT
CLASS="LITERAL"
>pg_ctl reload</TT
>). 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
<SPAN
CLASS="SYSTEMITEM"
>SIGHUP</SPAN
> processing.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CONFIG-SETTING-OTHER-METHODS"
>18.1.3. Other Ways to Set Parameters</A
></H2
><P
> A second way to set these configuration parameters is to give them
as a command-line option to the <TT
CLASS="COMMAND"
>postgres</TT
> command,
such as:
</P><PRE
CLASS="PROGRAMLISTING"
>postgres -c log_connections=yes -c log_destination='syslog'</PRE
><P>
Command-line options override any conflicting settings in
<TT
CLASS="FILENAME"
>postgresql.conf</TT
>. Note that this means you won't
be able to change the value on-the-fly by editing
<TT
CLASS="FILENAME"
>postgresql.conf</TT
>, so while the command-line
method might be convenient, it can cost you flexibility later.
</P
><P
> Occasionally it is useful to give a command line option to
one particular session only. The environment variable
<TT
CLASS="ENVAR"
>PGOPTIONS</TT
> can be used for this purpose on the
client side:
</P><PRE
CLASS="PROGRAMLISTING"
>env PGOPTIONS='-c geqo=off' psql</PRE
><P>
(This works for any <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>-based client application, not
just <SPAN
CLASS="APPLICATION"
>psql</SPAN
>.) Note that this won't work for
parameters that are fixed when the server is started or that must be
specified in <TT
CLASS="FILENAME"
>postgresql.conf</TT
>.
</P
><P
> 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 <A
HREF="sql-alterrole.html"
>ALTER ROLE</A
>
and <A
HREF="sql-alterdatabase.html"
>ALTER DATABASE</A
>,
respectively, are used to configure these settings. Per-database
settings override anything received from the
<TT
CLASS="COMMAND"
>postgres</TT
> command-line or the configuration
file, and in turn are overridden by per-user settings; both are
overridden by per-session settings.
</P
><P
> Some parameters can be changed in individual <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>
sessions with the <A
HREF="sql-set.html"
>SET</A
>
command, for example:
</P><PRE
CLASS="SCREEN"
>SET ENABLE_SEQSCAN TO OFF;</PRE
><P>
If <TT
CLASS="COMMAND"
>SET</TT
> is allowed, it overrides all other sources of
values for the parameter. Some parameters cannot be changed via
<TT
CLASS="COMMAND"
>SET</TT
>: for example, if they control behavior that
cannot be changed without restarting the entire
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server. Also, some parameters
require superuser permission to change via <TT
CLASS="COMMAND"
>SET</TT
> or
<TT
CLASS="COMMAND"
>ALTER</TT
>.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CONFIG-SETTING-EXAMINING"
>18.1.4. Examining Parameter Settings</A
></H2
><P
> The <A
HREF="sql-show.html"
>SHOW</A
>
command allows inspection of the current values of all parameters.
</P
><P
> The virtual table <TT
CLASS="STRUCTNAME"
>pg_settings</TT
> also allows
displaying and updating session run-time parameters; see <A
HREF="view-pg-settings.html"
>Section 45.64</A
> for details and a description of the
different variable types and when they can be changed.
<TT
CLASS="STRUCTNAME"
>pg_settings</TT
> is equivalent to <TT
CLASS="COMMAND"
>SHOW</TT
>
and <TT
CLASS="COMMAND"
>SET</TT
>, 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 <TT
CLASS="COMMAND"
>SHOW</TT
>.
</P
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