Automatic Cleanup¶
The automatic cleanup process (autovacuum) in the system automatically runs the VACUUM and ANALYZE statements to reclaim the record space marked as deleted and update statistics about the table.
Note
autovacuum does not block service statements initiated by users. autovacuum and autoanalyze statements can be executed concurrently without conflicts. This function is supported only in version later than 8.2.1.300.
autovacuum¶
Parameter description: Specifies whether to start the automatic cleanup process (autovacuum). Ensure that the track_counts parameter is set to on before enabling the automatic cleanup process.
Type: SIGHUP
Value range: Boolean
on indicates the database automatic cleanup process is enabled.
off indicates that the database automatic cleanup process is disabled.
Default value: on
Note
Set autovacuum to on if you want to enable the function of automatically cleaning up two-phase transactions after the system recovers from faults.
If autovacuum is set to on and autovacuum_max_workers to 0, the autovacuum process will not be automatically performed and only abnormal two-phase transactions are cleaned up after the system recovers from faults.
If autovacuum is set to on and the value of autovacuum_max_workers is greater than 0, the system will automatically clean up two-phase transactions and processes after recovering from faults.
Important
Even if this parameter is set to off, the database initiates a cleanup process when transaction ID wraparound needs to be prevented. When a CREATE DATABASE or DROP DATABASE operation fails, the transaction may have been committed or rolled back on some nodes whereas some nodes are still in the prepared state. In this case, perform the following operations to manually restore the nodes:
Use the gs_clean tool (setting the option parameter to -N) to query the xid of the abnormal two-phase transaction and nodes in the prepared status.
Log in to the nodes whose transactions are in the prepared status. Administrators connect to an available database such as gaussdb to run the SET xc_maintenance_mode = on statement.
Commit or roll back the two-phase transaction based on the global transaction status.
autovacuum_mode¶
Parameter description: Specifies whether the autoanalyze or autovacuum function is enabled. This parameter is valid only when autovacuum is set to on.
Type: SIGHUP
Value range: 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_mode¶
Parameter description: Specifies the autoanalyze mode. This parameter is supported by version 8.2.0 or later clusters.
Type: USERSET
Value range: enumerated values
normal indicates common autoanalyze.
light indicates lightweight autoanalyze.
Default value:
If the current cluster is upgraded from an earlier version to 8.2.0, the default value is normal to ensure forward compatibility.
If the cluster version 8.2.0 is newly installed, the default value is light.
autoanalyze_timeout¶
Parameter description: Specifies the timeout period of autoanalyze. If the duration of analyze on a table exceeds the value of autoanalyze_timeout, analyze is automatically canceled.
Type: SIGHUP
Value range: an integer ranging from 0 to 2147483. The unit is second.
Default value: 5min
analyze_stats_mode¶
Parameter description: Specifies the mode for ANALYZE to calculate statistics.
Type: USERSET
Value range: enumerated values
memory indicates that the memory is forcibly used to calculate statistics. Multi-column statistics are not calculated.
sample_table indicates that temporary sampling tables are forcibly used to calculate statistics. Temporary tables do not support this mode.
dynamic indicates that the statistics calculation mode is determined based on the size of maintenance_work_mem. If maintenance_work_mem can store samples, the memory mode is used. Otherwise, the temporary sampling table mode is used.
Default value:
If the current cluster is upgraded from an earlier version to 8.2.0.100, the default value is memory to ensure forward compatibility.
If the cluster version 8.2.0.100 is newly installed, the default value is dynamic.
analyze_sample_mode¶
Parameter description: Specifies the sampling model used by ANALYZE.
Type: USERSET
Value range: an integer ranging from 0 to 2
0 indicates the default reservoir sampling.
1 indicates the optimized reservoir sampling.
2 indicates range sampling.
Default value: 0
autovacuum_io_limits¶
Parameter description: Specifies the upper limit of I/Os triggered by the autovacuum process per second. This parameter has been discarded in version 8.1.2 and is reserved for compatibility with earlier versions. This parameter is invalid in the current version.
Type: SIGHUP
Value range: an integer ranging from -1 to 1073741823. -1 indicates that the default Cgroup is used.
Default value: -1
autovacuum_max_workers¶
Parameter description: Specifies the maximum number of automatic cleanup threads running at the same time.
Type: SIGHUP
Value range: an integer ranging from 0 to 128. 0 indicates that autovacuum is disabled.
Default value: 4
Note
This parameter works with autovacuum. The rules for clearing system catalogs and user tables are as follows:
When autovacuum_max_workers is set to 0, autovacuum is disabled and no tables are cleared.
If autovacuum_max_workers > 0 and autovacuum = off are configured, the system only clears the system catalogs and column-store tables with delta tables enabled (such as vacuum delta tables, vacuum cudesc tables, and delta merge).
When autovacuum_max_workers is set to a value greater than zero and autovacuum is enabled, all tables will be cleared.
autovacuum_naptime¶
Parameter description: Specifies the interval between two automatic cleanup operations.
Type: SIGHUP
Value range: an integer ranging from 1 to 2147483. The unit is second.
Default value: 60s
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.
Type: SIGHUP
Value range: an integer ranging from 0 to INT_MAX
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.
Type: SIGHUP
Value range: an integer ranging from 0 to INT_MAX
Default value:
If the current cluster is upgraded from an earlier version to 8.1.3, the default value is 10000 to ensure forward compatibility.
If the current cluster version is 8.1.3, the default value is 50.
autovacuum_vacuum_scale_factor¶
Parameter description: Specifies the size scaling factor of a table added to the autovacuum_vacuum_threshold parameter when a VACUUM event is triggered.
Type: SIGHUP
Value range: a floating point number ranging from 0.0 to 100.0
Default value: 0.2
autovacuum_analyze_scale_factor¶
Parameter description: Specifies the size scaling factor of a table added to the autovacuum_analyze_threshold parameter when an ANALYZE event is triggered.
Type: SIGHUP
Value range: a floating point number ranging from 0.0 to 100.0
Default value:
If the current cluster is upgraded from an earlier version to 8.1.3, the default value is 0.25 to ensure forward compatibility.
If the current cluster version is 8.1.3, the default value is 0.1.
autovacuum_freeze_max_age¶
Parameter description: Specifies the maximum age (in transactions) that a table's pg_class.relfrozenxid column can attain before a VACUUM operation is forced to prevent transaction ID wraparound within the table.
The old files under the subdirectory of pg_clog/ can also be deleted by the VACUUM operation. Even if the automatic cleanup process is forbidden, the system will invoke the automatic cleanup process to prevent the cyclic repetition.
Type: SIGHUP
Value range: an integer ranging from 100000 to 576460752303423487
Default value: 4000000000
autovacuum_vacuum_cost_delay¶
Parameter description: Specifies the value of the cost delay used in the autovacuum operation.
Type: SIGHUP
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: 2ms
autovacuum_vacuum_cost_limit¶
Parameter description: Specifies the value of the cost limit used in the autovacuum operation.
Type: SIGHUP
Value range: an integer ranging from -1 to 10000. -1 indicates that the normal vacuum cost limit is used.
Default value: -1
enable_pg_stat_object¶
Parameter description: Specifies whether AUTO VACUUM updates the PG_STAT_OBJECT system catalog. This parameter is supported by version 8.2.1 or later clusters.
Type: USERSET
Value range: Boolean
on indicates that the PG_STAT_OBJECT system catalog is updated during AUTO VACUUM.
off indicates that the PG_STAT_OBJECT system catalog is not updated during AUTO VACUUM.
Default value: on