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>Chapter 27. Monitoring Database Activity</TD
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><A
NAME="MONITORING-PS"
>27.1. Standard Unix Tools</A
></H1
><P
>   On most Unix platforms, <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> modifies its
   command title as reported by <TT
CLASS="COMMAND"
>ps</TT
>, 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: writer process
postgres  15555  0.0  0.0  57536   916 ?        Ss   18:02   0:00 postgres: checkpointer process
postgres  15556  0.0  0.0  57536   916 ?        Ss   18:02   0:00 postgres: wal writer process
postgres  15557  0.0  0.0  58504  2244 ?        Ss   18:02   0:00 postgres: autovacuum launcher process
postgres  15558  0.0  0.0  17512  1068 ?        Ss   18:02   0:00 postgres: stats collector process
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 <TT
CLASS="COMMAND"
>ps</TT
> 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 five
   processes are background worker processes automatically launched by the
   master process.  (The <SPAN
CLASS="QUOTE"
>"stats collector"</SPAN
> process will not be present
   if you have set the system not to start the statistics collector; likewise
   the <SPAN
CLASS="QUOTE"
>"autovacuum launcher"</SPAN
> 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

</P><PRE
CLASS="SCREEN"
>postgres: <TT
CLASS="REPLACEABLE"
><I
>user</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>database</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>host</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>activity</I
></TT
></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 <TT
CLASS="LITERAL"
>idle</TT
> (i.e., waiting for a client command),
  <TT
CLASS="LITERAL"
>idle in transaction</TT
> (waiting for client inside a <TT
CLASS="COMMAND"
>BEGIN</TT
> block),
  or a command type name such as <TT
CLASS="LITERAL"
>SELECT</TT
>.  Also,
  <TT
CLASS="LITERAL"
>waiting</TT
> 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
HREF="view-pg-locks.html"
><TT
CLASS="STRUCTNAME"
>pg_locks</TT
></A
>
  system view to determine who is blocking whom.)
  </P
><P
>   If you have turned off <A
HREF="runtime-config-statistics.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"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>  <SPAN
CLASS="PRODUCTNAME"
>Solaris</SPAN
> requires special handling. You must
  use <TT
CLASS="COMMAND"
>/usr/ucb/ps</TT
>, rather than
  <TT
CLASS="COMMAND"
>/bin/ps</TT
>. You also must use two <TT
CLASS="OPTION"
>w</TT
>
  flags, not just one. In addition, your original invocation of the
  <TT
CLASS="COMMAND"
>postgres</TT
> command must have a shorter
  <TT
CLASS="COMMAND"
>ps</TT
> status display than that provided by each
  server process.  If you fail to do all three things, the <TT
CLASS="COMMAND"
>ps</TT
>
  output for each server process will be the original <TT
CLASS="COMMAND"
>postgres</TT
>
  command line.
  </P
></BLOCKQUOTE
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