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<chapter id="monitoring">

<title>Monitoring Database Activity</title>

$ 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 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

</para>

<para>

The statistics collector communicates with the backends needing

The statistics collector communicates with the backends needing

information (including autovacuum) through temporary files.

These files are stored in the <filename>pg_stat_tmp</filename> subdirectory.

When the postmaster shuts down, a permanent copy of the statistics

<entry><structname>pg_stat_activity</></entry>

<entry>One row per server process, showing database OID, database

name, process <acronym>ID</>, user OID, user name, application name,

current query, query'swaiting status, time at which thecurrent

transaction and current query began execution,time at which the

process was started, andclient's address and port number.

client'saddress and port number, times at which theserver process,

currenttransaction, and current query began execution,process's waiting

status, andtext of the current query.

The columns that report data on the current query are available unless

the parameter <varname>track_activities</varname> has been turned off.

Furthermore, these columns are only visible if the user examining

Beginning in <productname>PostgreSQL</productname> 8.1, indexes can be

used either directly or via <quote>bitmap scans</>. In a bitmap scan

the output of several indexes can be combined via AND or OR rules;

so it is difficult to associate individual heap row fetches

so it is difficult to associate individual heap row fetches

with specific indexes when a bitmap scan is used. Therefore, a bitmap

scan increments the

<structname>pg_stat_all_indexes</>.<structfield>idx_tup_read</>

<entry>

Returns a record of information about the backend with the specified pid, or

one record for each active backend in the system if <symbol>NULL</symbol> is

specified. The fields returned arethe same asin the

specified. The fields returned area subset of thosein the

<structname>pg_stat_activity</structname> view.

</entry>

</row>