-
+
Server Configuration
Query and Index Statistics Collector
- These parameters control a server-wide statistics collection feature.
+ These parameters control server-wide statistics collection features.
When statistics collection is enabled, the data that is produced can be
accessed via the pg_stat and
pg_statio family of system views.
Refer to for more information.
-
- stats_command_string controls a separate data
- collection mechanism that can be turned on or off independently
- of whether the statistics-collection subprocess is running.
- The subprocess is only needed to support collection of
- block-level or row-level statistics.
-
-
-
- stats-command-string" xreflabel="stats_command_string">
- stats_command_string (boolean)
+ track-activities" xreflabel="track_activities">
+ track_activities (boolean)
-
stats_command_string> configuration parameter
+
track_activities> configuration parameter
-
- update_process_title (boolean)
-
-
update_process_title> configuration parameter
-
-
- Enables updating of the process title every time a new SQL command
- is received by the server. The process title is typically viewed
- by the
ps> command or in Windows using the Process
- Explorer>. Only superusers can change this setting.
-
-
-
-
-
- stats_start_collector (boolean)
-
-
stats_start_collector> configuration parameter
-
-
- Controls whether the server should start the
- statistics-collection subprocess. This is on by default, but
- can be turned off if you know you have no interest in
- collecting statistics or running autovacuum.
- This parameter can only be set at server start, because the collection
- subprocess cannot be started or stopped on-the-fly. (However, the
- extent to which statistics are actually gathered can be changed while
- the server is running, so long as the subprocess exists.)
-
-
-
-
-
- stats_block_level (boolean)
-
-
stats_block_level> configuration parameter
-
-
- Enables the collection of block-level statistics on database
- activity. This parameter is off by default.
- Only superusers can change this setting.
-
-
-
-
-
- stats_row_level (boolean)
+
+ track_counts (boolean)
-
stats_row_level> configuration parameter
+
track_counts> configuration parameter
- Enables the collection of row-level statistics on database
- activity. This parameter is on by default, because the autovacuum
+ Enables collection of statistics on database activity.
+ This parameter is on by default, because the autovacuum
daemon needs the collected information.
Only superusers can change this setting.
- stats-reset-on-server-start" xreflabel="stats_reset_on_server_start">
- stats_reset_on_server_start (boolean)
+ update-process-title" xreflabel="update_process_title">
+ update_process_title (boolean)
-
stats_reset_on_server_start> configuration parameter
+
update_process_title> configuration parameter
- If on, collected block-level and row-level statistics are zeroed out
- whenever the server is restarted. If off, statistics are accumulated
- across server restarts. This parameter is off by default.
- This parameter can only be set at server start.
+ Enables updating of the process title every time a new SQL command
+ is received by the server. The process title is typically viewed
+ by the ps> command,
+ or in Windows by using the
Process Explorer>.
+ Only superusers can change this setting.
Controls whether the server should run the
- autovacuum launcher daemon. This is on by default.
- <varname>stats_start_collector> and stats_row_level>
- must also be turned on for autovacuum to work.
+ autovacuum launcher daemon. This is on by default; however,
+ <xref linkend="guc-track-counts"> must also be turned on for
+ autovacuum to work.
This parameter can only be set in the postgresql.conf>
file or on the server command line.
Note that even when this parameter is disabled, the system
- will periodically launch autovacuum processes in order to
+ will launch autovacuum processes if necessary to
prevent transaction ID wraparound. See
linkend="vacuum-for-wraparound"> for more information.
- autovacuum-max-workers" xreflabel="autovacuum_max_workers">
- autovacuum_max_workers (integer)
+ log-autovacuum-min-duration" xreflabel="log_autovacuum_min_duration">
+ log_autovacuum_min_duration (integer)
-
autovacuum_max_workers> configuration parameter
+
log_autovacuum_min_duration> configuration parameter
- Specifies the maximum number of autovacuum processes (other than the
- autovacuum launcher) which may be running at any one time. The default
- is three (3). This parameter can only be set in
+ Causes each action executed by autovacuum to be logged if it ran for at
+ least the specified number of milliseconds. Setting this to zero logs
+ all autovacuum actions. Minus-one (the default) disables logging
+ autovacuum actions. For example, if you set this to
+ 250ms then all automatic vacuums and analyzes that run
+ 250ms or longer will be logged. Enabling this parameter can be helpful
+ in tracking autovacuum activity. This setting can only be set in
the postgresql.conf> file or on the server command line.
- log-autovacuum" xreflabel="log_autovacuum">
- log_autovacuum (integer)
+ autovacuum-max-workers" xreflabel="autovacuum_max_workers">
+ autovacuum_max_workers (integer)
-
log_autovacuum> configuration parameter
+
autovacuum_max_workers> configuration parameter
- Causes each action executed by autovacuum to be logged if it ran for at
- least the specified number of milliseconds. Setting this to zero logs
- all autovacuum actions. Minus-one (the default) disables logging
- autovacuum actions. For example, if you set this to
- 250ms then all vacuums and analyzes that run
- 250ms or longer will be logged. Enabling this parameter can be helpful
- in tracking autovacuum activity. This setting can only be set in
+ Specifies the maximum number of autovacuum processes (other than the
+ autovacuum launcher) which may be running at any one time. The default
+ is three. This parameter can only be set in
the postgresql.conf> file or on the server command line.
-
+
Routine Database Maintenance Tasks
-
Updating planner statistics
+
Updating Planner Statistics
-
Preventing transaction ID wraparound failures
+
Preventing Transaction ID Wraparound Failures
-
The auto-vacuum daemon
+
The Auto-Vacuum Daemon
VACUUM and ANALYZE commands.
When enabled, autovacuum checks for
tables that have had a large number of inserted, updated or deleted
- tuples. These checks use the row-level statistics collection facility;
+ tuples. These checks use the statistics collection facility;
therefore, autovacuum cannot be used unless
- linkend="guc-stats-start-collector"> and
- linkend="guc-stats-row-level"> are set to true.
+ linkend="guc-track-counts"> is set to true.
In the default configuration, autovacuuming is enabled and the related
configuration parameters are appropriately set.
eligible for vacuuming in a short amount of time, all autovacuum workers
may end up vacuuming those tables for a very long time. This would result
in other tables and databases not being vacuumed until a worker became
- available. There is also not a limit on how many workers might be in a
- single database, but workers do try and avoid repeating work that has
+ available. There is not a limit on how many workers might be in a
+ single database, but workers do try to avoid repeating work that has
already been done by other workers. Note that the number of running
workers does not count towards the nor
the limits.
-
+
Monitoring Database Activity
PostgreSQL's
statistics collector>
is a subsystem that supports collection and reporting of information about
server activity. Presently, the collector can count accesses to tables
- and indexes in both disk-block and individual-row terms.
+ and indexes in both disk-block and individual-row terms. It also tracks
+ total numbers of rows in each table, and the last vacuum and analyze times
+ for each table.
PostgreSQL also supports determining the exact
command currently being executed by other server processes. This is an
- independent facility that can be enabled or disabled whether or not
- block-level and row-level statistics are being collected.
+ independent facility that does not depend on the collector process.
- The parameter must be
- set to true> for the statistics collector to be launched
- at all. This is the default and recommended setting, but it can be
- turned off if you have no interest in statistics and want to
- squeeze out every last drop of overhead. (The savings is likely to
- be small, however.) Note that this option cannot be changed while
- the server is running.
+ The parameter controls whether
+ information is actually sent to the collector process and thus determines
+ whether any run-time overhead occurs for event counting.
- The parameters
and
- linkend="guc-stats-row-level"> control how much information is
- actually sent to the collector and thus determine how much run-time
- overhead occurs. These respectively determine whether a server
- process tracks disk-block-level access
- statistics and row-level access statistics and sends these to the collector.
- Additionally, per-database transaction commit and abort statistics
- are collected if either of these parameters are set.
-
-
- The parameter enables monitoring
+ The parameter enables monitoring
of the current command being executed by any server process.
- The statistics collector subprocess need not be running to enable this
- feature.
When using the statistics to monitor current activity, it is important
to realize that the information does not update instantaneously.
- Each individual server process transmits new block and row access counts to
+ Each individual server process transmits new statistical counts to
the collector just before going idle; so a query or transaction still in
progress does not affect the displayed totals. Also, the collector itself
emits a new report at most once per PGSTAT_STAT_INTERVAL
milliseconds (500 unless altered while building the server). So the
displayed information lags behind actual activity. However, current-query
- information collected by stats_command_string is
+ information collected by track_activities is
always up-to-date.
current query began execution, time at which the process was
started, and client's address and port number. The columns that
report data on the current query are available unless the parameter
- stats_command_string has been turned off.
+ track_activities has been turned off.
Furthermore, these columns are only visible if the user examining
the view is a superuser or the same as the user owning the process
being reported on.
Active command of the given server process, but only if the
current user is a superuser or the same user as that of
the session being queried (and
- stats_command_string is on)
+ track_activities is on)
True if the given server process is waiting for a lock,
but only if the current user is a superuser or the same user as that of
the session being queried (and
- stats_command_string is on)
+ track_activities is on)
executing query was started, but only if the
current user is a superuser or the same user as that of
the session being queried (and
- stats_command_string is on)
+ track_activities is on)
executing transaction was started, but only if the
current user is a superuser or the same user as that of
the session being queried (and
- stats_command_string is on)
+ track_activities is on)