On most Unix platforms, PostgreSQL modifies its command title as reported by
ps, so that individual server processes can readily be identified. A sample display is
$ 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 15558 0.0 0.0 17512 1068 ? Ss 18:02 0:00 postgres: stats collector 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
(The appropriate invocation of
ps 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 five processes are background worker processes automatically launched by the primary process. (The “stats collector” process will not be present if you have set the system not to start the statistics collector; likewise the “autovacuum launcher” process can be disabled.) Each of the remaining processes is a server process handling one client connection. Each such process sets its command line display in the form
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
idle (i.e., waiting for a client command),
idle in transaction (waiting for client inside a
BEGIN block), or a command type name such as
waiting 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
pg_locks system view to determine who is blocking whom.)
If cluster_name has been configured the cluster name will also be shown in
$ 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 ...
If you have turned off update_process_title 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.
Solaris requires special handling. You must use
/usr/ucb/ps, rather than
/bin/ps. You also must use two
w flags, not just one. In addition, your original invocation of the
postgres command must have a shorter
ps status display than that provided by each server process. If you fail to do all three things, the
ps output for each server process will be the original
postgres command line.
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