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On most Unix platforms, <span class="productname">PostgreSQL</span> modifies its
command title as reported by <code class="command">ps</code>, so that individual server
processes can readily be identified. A sample display is
</p><pre class="screen">
$ ps auxww | grep ^postgres
postgres 15551 0.0 0.1 57536 7132 pts/0 S 18:02 0:00 postgres -i
postgres 15554 0.0 0.0 57536 1184 ? Ss 18:02 0:00 postgres: background writer
postgres 15555 0.0 0.0 57536 916 ? Ss 18:02 0:00 postgres: checkpointer
postgres 15556 0.0 0.0 57536 916 ? Ss 18:02 0:00 postgres: walwriter
postgres 15557 0.0 0.0 58504 2244 ? Ss 18:02 0:00 postgres: autovacuum launcher
postgres 15582 0.0 0.0 58772 3080 ? Ss 18:04 0:00 postgres: joe runbug 127.0.0.1 idle
postgres 15606 0.0 0.0 58772 3052 ? Ss 18:07 0:00 postgres: tgl regression [local] SELECT waiting
postgres 15610 0.0 0.0 58772 3056 ? Ss 18:07 0:00 postgres: tgl regression [local] idle in transaction
</pre><p>
(The appropriate invocation of <code class="command">ps</code> varies across different
platforms, as do the details of what is shown. This example is from a
recent Linux system.) The first process listed here is the
primary server process. The command arguments
shown for it are the same ones used when it was launched. The next four
processes are background worker processes automatically launched by the
primary process. (The <span class="quote">“<span class="quote">autovacuum launcher</span>”</span> process will not
be present if you have set the system not to run autovacuum.)
Each of the remaining
processes is a server process handling one client connection. Each such
process sets its command line display in the form
</p><pre class="screen">
postgres: <em class="replaceable"><code>user</code></em> <em class="replaceable"><code>database</code></em> <em class="replaceable"><code>host</code></em> <em class="replaceable"><code>activity</code></em>
</pre><p>
The user, database, and (client) host items remain the same for
the life of the client connection, but the activity indicator changes.
The activity can be <code class="literal">idle</code> (i.e., waiting for a client command),
<code class="literal">idle in transaction</code> (waiting for client inside a <code class="command">BEGIN</code> block),
or a command type name such as <code class="literal">SELECT</code>. Also,
<code class="literal">waiting</code> is appended if the server process is presently waiting
on a lock held by another session. In the above example we can infer
that process 15606 is waiting for process 15610 to complete its transaction
and thereby release some lock. (Process 15610 must be the blocker, because
there is no other active session. In more complicated cases it would be
necessary to look into the
<a class="link" href="view-pg-locks.html" title="54.12. pg_locks"><code class="structname">pg_locks</code></a>
system view to determine who is blocking whom.)
</p><p>
If <a class="xref" href="runtime-config-logging.html#GUC-CLUSTER-NAME">cluster_name</a> has been configured the
cluster name will also be shown in <code class="command">ps</code> output:
</p><pre class="screen">
$ psql -c 'SHOW cluster_name'
cluster_name
--------------
server1
(1 row)
$ ps aux|grep server1
postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: server1: background writer
...
</pre><p>
</p><p>
If you have turned off <a class="xref" href="runtime-config-logging.html#GUC-UPDATE-PROCESS-TITLE">update_process_title</a> then the
activity indicator is not updated; the process title is set only once
when a new process is launched. On some platforms this saves a measurable
amount of per-command overhead; on others it's insignificant.
</p><div class="tip"><h3 class="title">Tip</h3><p>
<span class="productname">Solaris</span> requires special handling. You must
use <code class="command">/usr/ucb/ps</code>, rather than
<code class="command">/bin/ps</code>. You also must use two <code class="option">w</code>
flags, not just one. In addition, your original invocation of the
<code class="command">postgres</code> command must have a shorter
<code class="command">ps</code> status display than that provided by each
server process. If you fail to do all three things, the <code class="command">ps</code>
output for each server process will be the original <code class="command">postgres</code>
command line.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="monitoring.html" title="Chapter 28. Monitoring Database Activity">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="monitoring.html" title="Chapter 28. Monitoring Database Activity">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="monitoring-stats.html" title="28.2. The Cumulative Statistics System">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 28. Monitoring Database Activity </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 28.2. The Cumulative Statistics System</td></tr></table></div></body></html>
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