18.9. Run-time Statistics
18.9.1. Query and Index Statistics Collector
These parameters control server-wide statistics collection features. When statistics collection is enabled, the data that is produced can be accessed via the
pg_statio family of system views. Refer to Chapter 26 for more information.
Enables the collection of information on the currently executing command of each session, along with its identifier and the time when that command began execution. This parameter is on by default. Note that even when enabled, this information is not visible to all users, only to superusers, roles with privileges of the
pg_read_all_statsrole and the user owning the sessions being reported on (including sessions belonging to a role they have the privileges of), so it should not represent a security risk. Only superusers can change this setting.
Specifies the amount of memory reserved to store the text of the currently executing command for each active session, for the
queryfield. If this value is specified without units, it is taken as bytes. The default value is 1024 bytes. This parameter can only be set at server start.
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.
Enables timing of database I/O calls. This parameter is off by default, as it will repeatedly query the operating system for the current time, which may cause significant overhead on some platforms. You can use the pg_test_timing tool to measure the overhead of timing on your system. I/O timing information is displayed in
pg_stat_database, in the output of EXPLAIN when the
BUFFERSoption is used, by autovacuum for auto-vacuums and auto-analyzes, when log_autovacuum_min_duration is set and by pg_stat_statements. Only superusers can change this setting.
Enables timing of WAL I/O calls. This parameter is off by default, as it will repeatedly query the operating system for the current time, which may cause significant overhead on some platforms. You can use the pg_test_timing tool to measure the overhead of timing on your system. I/O timing information is displayed in
pg_stat_wal. Only superusers can change this setting.
Enables tracking of function call counts and time used. Specify
plto track only procedural-language functions,
allto also track SQL and C language functions. The default is
none, which disables function statistics tracking. Only superusers can change this setting.
SQL-language functions that are simple enough to be “inlined” into the calling query will not be tracked, regardless of this setting.
Sets the directory to store temporary statistics data in. This can be a path relative to the data directory or an absolute path. The default is
pg_stat_tmp. Pointing this at a RAM-based file system will decrease physical I/O requirements and can lead to improved performance. This parameter can only be set in the
postgresql.conffile or on the server command line.
18.9.2. Statistics Monitoring
Enables in-core computation of a query identifier. Query identifiers can be displayed in the
EXPLAIN, or emitted in the log if configured via the log_line_prefix parameter. The pg_stat_statements extension also requires a query identifier to be computed. Note that an external module can alternatively be used if the in-core query identifier computation method is not acceptable. In this case, in-core computation must be always disabled. Valid values are
auto, which lets modules such as pg_stat_statements automatically enable it, and
regresswhich has the same effect as
auto, except that the query identifier is not shown in the
EXPLAINoutput in order to facilitate automated regression testing. The default is
To ensure that only one query identifier is calculated and displayed, extensions that calculate query identifiers should throw an error if a query identifier has already been computed.
For each query, output performance statistics of the respective module to the server log. This is a crude profiling instrument, similar to the Unix
getrusage()operating system facility.
log_statement_statsreports total statement statistics, while the others report per-module statistics.
log_statement_statscannot be enabled together with any of the per-module options. All of these options are disabled by default. Only superusers can change these settings.