log_line_prefix

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<p>
         This is a <code class="function">printf</code>-style string that is output at the
         beginning of each log entry that is sent to <code class="literal">stderr</code>,
         <code class="literal">syslog</code>, or <code class="literal">eventlog</code>.
         <code class="literal">%</code> characters begin <span class="quote">“<span class="quote">escape sequences</span>”</span>
         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 will be treated as empty by
         background processes such as the main server process. Status
         information may be aligned either left or right by specifying a
         numeric literal after the % and before the option. A negative
         value will cause the status information to be padded on the
         right with spaces to give it a minimum width, whereas a positive
         value will pad on the left. Padding can be useful to aid human
         readability in log files.
       </p><p>
         This parameter can only be set in the <code class="filename">postgresql.conf</code>
         file or on the server command line. The default is
         <code class="literal">'%m [%p] '</code> which logs a time stamp and the process ID.
       </p><div class="informaltable"><table border="1" class="informaltable"><colgroup><col/><col/><col/></colgroup><thead><tr><th>Escape</th><th>Effect</th><th>Session only</th></tr></thead><tbody><tr><td><code class="literal">%a</code></td><td>Application name</td><td>yes</td></tr><tr><td><code class="literal">%u</code></td><td>User name</td><td>yes</td></tr><tr><td><code class="literal">%d</code></td><td>Database name</td><td>yes</td></tr><tr><td><code class="literal">%r</code></td><td>Remote host name or IP address, and remote port</td><td>yes</td></tr><tr><td><code class="literal">%h</code></td><td>Remote host name or IP address</td><td>yes</td></tr><tr><td><code class="literal">%L</code></td><td>Local address (the IP address on the server that the
             client connected to)</td><td>yes</td></tr><tr><td><code class="literal">%b</code></td><td>Backend type</td><td>no</td></tr><tr><td><code class="literal">%p</code></td><td>Process ID</td><td>no</td></tr><tr><td><code class="literal">%P</code></td><td>Process ID of the parallel group leader, if this process
              is a parallel query worker</td><td>no</td></tr><tr><td><code class="literal">%t</code></td><td>Time stamp without milliseconds</td><td>no</td></tr><tr><td><code class="literal">%m</code></td><td>Time stamp with milliseconds</td><td>no</td></tr><tr><td><code class="literal">%n</code></td><td>Time stamp with milliseconds (as a Unix epoch)</td><td>no</td></tr><tr><td><code class="literal">%i</code></td><td>Command tag: type of session's current command</td><td>yes</td></tr><tr><td><code class="literal">%e</code></td><td>SQLSTATE error code</td><td>no</td></tr><tr><td><code class="literal">%c</code></td><td>Session ID: see below</td><td>no</td></tr><tr><td><code class="literal">%l</code></td><td>Number of the log line for each session or process, starting at 1</td><td>no</td></tr><tr><td><code class="literal">%s</code></td><td>Process start time stamp</td><td>no</td></tr><tr><td><code class="literal">%v</code></td><td>Virtual transaction ID (procNumber/localXID);  see
             <a class="xref" href="/docs/18/transaction-id.html" title="67.1. Transactions and Identifiers">Section 67.1</a></td><td>no</td></tr><tr><td><code class="literal">%x</code></td><td>Transaction ID (0 if none is assigned);  see
             <a class="xref" href="/docs/18/transaction-id.html" title="67.1. Transactions and Identifiers">Section 67.1</a></td><td>no</td></tr><tr><td><code class="literal">%q</code></td><td>Produces no output, but tells non-session
             processes to stop at this point in the string; ignored by
             session processes</td><td>no</td></tr><tr><td><code class="literal">%Q</code></td><td>Query identifier of the current query.  Query
             identifiers are not computed by default, so this field
             will be zero unless <a class="xref" href="/docs/18/runtime-config-statistics.html#GUC-COMPUTE-QUERY-ID">compute_query_id</a>
             parameter is enabled or a third-party module that computes
             query identifiers is configured.</td><td>yes</td></tr><tr><td><code class="literal">%%</code></td><td>Literal <code class="literal">%</code></td><td>no</td></tr></tbody></table></div><p>
          The backend type corresponds to the column
          <code class="structfield">backend_type</code> in the view
          <a class="link" href="/docs/18/monitoring-stats.html#MONITORING-PG-STAT-ACTIVITY-VIEW" title="27.2.3. pg_stat_activity">
<code class="structname">pg_stat_activity</code></a>,
          but additional types can appear
          in the log that don't show in that view.
         </p><p>
         The <code class="literal">%c</code> 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 process start time and the
         process ID, so <code class="literal">%c</code> can also be used as a space saving way
         of printing those items.  For example, to generate the session
         identifier from <code class="literal">pg_stat_activity</code>, use this query:
</p><pre class="programlisting">
SELECT to_hex(trunc(EXTRACT(EPOCH FROM backend_start))::integer) || '.' ||
       to_hex(pid)
FROM pg_stat_activity;
</pre><p>
</p><div class="tip"><h3 class="title">Tip</h3><p>
         If you set a nonempty value for <code class="varname">log_line_prefix</code>,
         you should usually make its last character be a space, to provide
         visual separation from the rest of the log line.  A punctuation
         character can be used too.
        </p></div><div class="tip"><h3 class="title">Tip</h3><p>
<span class="application">Syslog</span> produces its own
         time stamp and process ID information, so you probably do not want to
         include those escapes if you are logging to <span class="application">syslog</span>.
        </p></div><div class="tip"><h3 class="title">Tip</h3><p>
         The <code class="literal">%q</code> escape is useful when including information that is
         only available in session (backend) context like user or database
         name.  For example:
</p><pre class="programlisting">
log_line_prefix = '%m [%p] %q%u@%d/%a '
</pre><p>
</p></div><div class="note"><h3 class="title">Note</h3><p>
         The <code class="literal">%Q</code> escape always reports a zero identifier
         for lines output by <a class="xref" href="/docs/18/runtime-config-logging.html#GUC-LOG-STATEMENT">log_statement</a> because
         <code class="varname">log_statement</code> generates output before an
         identifier can be calculated, including invalid statements for
         which an identifier cannot be calculated.
        </p></div>

documentation revision

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