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<chapter Id="runtime-config">

<title>Server Configuration</title>

<listitem>

<para>

This is a <function>printf</>-style string that is output at the

beginning of each log line. The default is an empty string.

Each recognized escape is replaced as outlined

below - anything else that looks like an escape is ignored. Other

beginning of each log line.

<literal>%</> characters begin <quote>escape sequences</>

that are replaced with status information as outlined below.

Unrecognized escapes are ignored. Other

characters are copied straight to the log line. Some escapes are

only recognized by session processes, and do not apply to

background processes such as the main server process. <application>Syslog</>

produces its own

time stamp and process ID information, so you probably do not want to

use those escapes if you are using <application>syslog</>.

background processes such as the main server process.

This parameter can only be set in the <filename>postgresql.conf</>

file or on the server command line.

file or on the server command line. The default is an empty string.

<informaltable>

<tgroup cols="3">

</row>

<row>

<entry><literal>%t</literal></entry>

<entry>Time stamp(no milliseconds,no timezone on Windows)</entry>

<entry>Time stampwithout milliseconds (no timezone either on Windows)</entry>

<entry>no</entry>

</row>

<row>

</row>

<row>

<entry><literal>%i</literal></entry>

<entry>Command tag:This is the command that generated the log line.</entry>

<entry>Command tag:type of session's current command</entry>

<entry>yes</entry>

</row>

<row>

<entry><literal>%c</literal></entry>

<entry>Session ID: A unique identifier for each session.

It is 2 4-byte hexadecimal numbers (without leading zeros)

separated by a dot. The numbers

are the session start time and the process ID, so this can also

be used as a space saving way of printing these items.</entry>

<entry>Session ID: see below</entry>

<entry>yes</entry>

</row>

<row>

</row>

<row>

<entry><literal>%q</literal></entry>

<entry>Does not produce any output, but tells non-session

processes to stop at this point in the string. Ignored by

session processes.</entry>

<entry>Produces no output, but tells non-session

processes to stop at this point in the string; ignored by

session processes</entry>

<entry>no</entry>

</row>

<row>

</tbody>

</tgroup>

</informaltable>

The <literal>%c</> escape prints a quasi-unique session identifier,

consisting of two 4-byte hexadecimal numbers (without leading zeros)

separated by a dot. The numbers are the session start time and the

process ID, so <literal>%c</> can also be used as a space saving way

of printing those items.

</para>

<tip>

<para>

If you set a nonempty value for <varname>log_line_prefix</>,

you should usually make its last character be a space, to provide

visual separation from the rest of the log line. A punctuation

character could be used too.

</para>

</tip>

<tip>

<para>

<application>Syslog</> produces its own

time stamp and process ID information, so you probably do not want to

use those escapes if you are logging to <application>syslog</>.

</para>

</tip>

</listitem>

</varlistentry>