27.1. Standard Unix Tools

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   960  0.0  1.1  6104 1480 pts/1    SN   13:17   0:00 postgres -i
postgres   963  0.0  1.1  7084 1472 pts/1    SN   13:17   0:00 postgres: writer process
postgres   965  0.0  1.1  6152 1512 pts/1    SN   13:17   0:00 postgres: stats collector process
postgres   998  0.0  2.3  6532 2992 pts/1    SN   13:18   0:00 postgres: tgl runbug 127.0.0.1 idle
postgres  1003  0.0  2.4  6532 3128 pts/1    SN   13:19   0:00 postgres: tgl regression [local] SELECT waiting
postgres  1016  0.1  2.4  6532 3080 pts/1    SN   13:19   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 master server process. The command arguments shown for it are the same ones used when it was launched. The next two processes are background worker processes automatically launched by the master process. (The "stats collector" process will not be present if you have set the system not to start the statistics collector.) Each of the remaining processes is a server process handling one client connection. Each such process sets its command line display in the form

postgres: user database host activity

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 SELECT. Also, 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 1003 is waiting for process 1016 to complete its transaction and thereby release some lock.

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.