These parameters control the server-wide cumulative statistics system.
      When enabled, the data that is collected can be accessed via the
      pg_stat and pg_statio
      family of system views.  Refer to Chapter 27 for more
      information.
     
track_activities (boolean)
      
       #
        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 only
        visible to superusers, roles with privileges of the
        pg_read_all_stats role 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 and users with the appropriate SET
        privilege can change this setting.
       
track_activity_query_size (integer)
      
       #
       Specifies the amount of memory reserved to store the text of the
       currently executing command for each active session, for the
       pg_stat_activity.query field.
       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.
       
track_counts (boolean)
      
       #
        Enables collection of statistics on database activity.
        This parameter is on by default, because the autovacuum
        daemon needs the collected information.
        Only superusers and users with the appropriate SET
        privilege can change this setting.
       
track_io_timing (boolean)
      
       #
        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,
        
        pg_stat_io, in the output of
        EXPLAIN when the BUFFERS option
        is used, in the output of VACUUM when
        the VERBOSE option is used, by autovacuum
        for auto-vacuums and auto-analyzes, when log_autovacuum_min_duration is set and by
        pg_stat_statements.
        Only superusers and users with the appropriate SET
        privilege can change this setting.
       
track_wal_io_timing (boolean)
      
       #
        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 and users with the appropriate SET
        privilege can change this setting.
       
track_functions (enum)
      
       #
        Enables tracking of function call counts and time used. Specify
        pl to track only procedural-language functions,
        all to also track SQL and C language functions.
        The default is none, which disables function
        statistics tracking.
        Only superusers and users with the appropriate SET
        privilege 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.
stats_fetch_consistency (enum)
      
       #
        Determines the behavior when cumulative statistics are accessed
        multiple times within a transaction. When set to
        none, each access re-fetches counters from shared
        memory. When set to cache, the first access to
        statistics for an object caches those statistics until the end of the
        transaction unless pg_stat_clear_snapshot() is
        called. When set to snapshot, the first statistics
        access caches all statistics accessible in the current database, until
        the end of the transaction unless
        pg_stat_clear_snapshot() is called. Changing this
        parameter in a transaction discards the statistics snapshot.
        The default is cache.
       
         none is most suitable for monitoring systems. If
         values are only accessed once, it is the most
         efficient. cache ensures repeat accesses yield the
         same values, which is important for queries involving
         e.g. self-joins. snapshot can be useful when
         interactively inspecting statistics, but has higher overhead,
         particularly if many database objects exist.
        
compute_query_id (enum)
      
       #
        Enables in-core computation of a query identifier.
        Query identifiers can be displayed in the pg_stat_activity
        view, using 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 off (always disabled),
        on (always enabled), auto,
        which lets modules such as pg_stat_statements
        automatically enable it, and regress which
        has the same effect as auto, except that the
        query identifier is not shown in the EXPLAIN output
        in order to facilitate automated regression testing.
        The default is auto.
       
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.
log_statement_stats (boolean)
      
      log_parser_stats (boolean)
      
      log_planner_stats (boolean)
      
      log_executor_stats (boolean)
      
       #
        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_stats reports total
        statement statistics, while the others report per-module statistics.
        log_statement_stats cannot be enabled together with
        any of the per-module options.  All of these options are disabled by
        default.
        Only superusers and users with the appropriate SET
        privilege can change these settings.