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Automatic Vacuuming

The autovacuum process automatically runs the VACUUM and ANALYZE statements to reclaim the record space marked as deleted and update statistics about the table.

autovacuum

Parameter description: Specifies whether to enable the autovacuum process in the database. Ensure that the track_counts parameter is set to on before enabling the automatic cleanup process.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

img NOTE:

  • Set the autovacuum parameter to on if you want to enable the automatic cleanup of abnormal two-phase transactions when the system recovers from faults.
  • If autovacuum is set to on and autovacuum_max_workers to 0, the autovacuum process is enabled only when the system recovers from faults to clean up abnormal two-phase transactions.
  • If autovacuum is set to on and autovacuum_max_workers to a value greater than 0, the autovacuum process is enabled to clean up bloated tables during daily operations and abnormal two-phase transactions when the system recovers from faults.

img NOTICE: Even if the autovacuum parameter is set to off, the autovacuum process will be enabled automatically when a transaction ID wraparound is about to occur. When a CREATE DATABASE or DROP DATABASE operation fails, it is possible that the transaction has been committed or rolled back on some nodes whereas some nodes are still in the prepared status.

Value range: Boolean

  • on indicates that the autovacuum process is enabled.
  • off indicates that the autovacuum process is disabled.

Default value:on

autovacuum_mode

Parameter description: Specifies whether the autoanalyze or autovacuum function is enabled. This parameter is valid only when autovacuum is set to on.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Valid value: enumerated values

  • analyze indicates that only autoanalyze is performed.
  • vacuum indicates that only autovacuum is performed.
  • mix indicates that both autoanalyze and autovacuum are performed.
  • none indicates that neither of them is performed.

Default value:mix

autoanalyze_timeout

Parameter description: Specifies the timeout period of autoanalyze. If the duration of autoanalyze on a table exceeds the value of autoanalyze_timeout, the autoanalyze is automatically canceled.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 0 to 2147483. The unit is s.

Default value:5min (300s)

autovacuum_io_limits

Parameter description: Specifies the upper limit of I/Os triggered by the autovacuum process per second.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer. The value can be –1 or a number ranging from 0 to 1073741823. –1 indicates that the default cgroup is used.

Default value:–1

log_autovacuum_min_duration

Parameter description: Records each step performed by the autovacuum process to the server log when the execution time of the autovacuum process is greater than or equal to a certain value. This parameter helps track the autovacuum behavior.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

A setting example is as follows:

Set the log_autovacuum_min_duration parameter to 250 ms to record the actions of autovacuum if it runs for 250 ms or longer.

Value range: an integer ranging from –1 to 2147483647. The unit is ms.

  • 0 indicates that all autovacuum actions are recorded in the log.
  • –1 indicates that all autovacuum actions are not recorded in the log.
  • A value other than –1 indicates that a message is recorded when an autovacuum action is skipped due to a lock conflict.

Default value:–1

autovacuum_max_workers

Parameter description: Specifies the maximum number of autovacuum worker threads that can run at the same time. The upper limit of this parameter is related to the values of max_connections and job_queue_processes.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer. The minimum value is 0, indicating that autovacuum is not enabled. The theoretical maximum value is 262143, but the actual maximum value is a dynamic value calculated by the following formula: 262143 - max_connections - job_queue_processes - Number of auxiliary threads - Number of autovacuum launcher threads - 1. The number of auxiliary threads and the number of autovacuum launcher threads are specified by two macros. Their default values are 20 and 2 respectively.

Default value:3

autovacuum_naptime

Parameter description: Specifies the interval between activity rounds for the autovacuum process.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 1 to 2147483. The unit is s.

Default value:10min (600s)

autovacuum_vacuum_threshold

Parameter description: Specifies the threshold for triggering the VACUUM operation. When the number of deleted or updated records in a table exceeds the specified threshold, the VACUUM operation is executed on this table.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 0 to 2147483647.

Default value:50

autovacuum_analyze_threshold

Parameter description: Specifies the threshold for triggering the ANALYZE operation. When the number of deleted, inserted, or updated records in a table exceeds the specified threshold, the ANALYZE operation is executed on this table.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from 0 to 2147483647

Default value:50

autovacuum_vacuum_scale_factor

Parameter description: Specifies a fraction of the table size added to the autovacuum_vacuum_threshold parameter when deciding whether to vacuum a table.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: a floating point number ranging from 0.0 to 100.0

Default value:0.2

autovacuum_analyze_scale_factor

Parameter description: Specifies a fraction of the table size added to the autovacuum_analyze_threshold parameter when deciding whether to analyze a table.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: a floating point number ranging from 0.0 to 100.0

Default value:0.1

autovacuum_freeze_max_age

Parameter description: Specifies the maximum age (in transactions) that a table's pg_class.relfrozenxid field can attain before a VACUUM operation is performed.

  • The old files under the subdirectory of pg_clog/ can also be deleted by the VACUUM operation.
  • Even if the autovacuum process is disabled, the system will invoke the process to prevent transaction ID wraparound.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer from 100000 to 576460752303423487

Default value:20000000000

autovacuum_vacuum_cost_delay

Parameter description: Specifies the value of the cost delay used in the autovacuum operation.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from –1 to 100. The unit is ms. –1 indicates that the normal vacuum cost delay is used.

Default value:20ms

autovacuum_vacuum_cost_limit

Parameter description: Specifies the value of the cost limit used in the autovacuum operation.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: an integer ranging from –1 to 10000 –1 indicates that the normal vacuum cost limit is used.

Default value:–1

defer_csn_cleanup_time

Parameter description: Specifies the interval of recycling transaction IDs.

Value range: an integer ranging from 0 to INT_MAX. The unit is ms.

Default value:5s (5000 ms)