Checkpoints

checkpoint_segments

Parameter description: Specifies the minimum number of WAL segment files in the period specified by checkpoint_timeout. The size of each log file is 16 MB.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer. The minimum value is 1.

Increasing the value of this parameter speeds up the export of a large amount of data. Set this parameter based on checkpoint_timeout and shared_buffers. This parameter affects the number of WAL segment files that can be reused. Generally, the maximum number of reused files in the pg_xlog folder is twice the number of checkpoint_segments. The reused files are not deleted and are renamed to the WAL segment files which will be later used.

Default value: 64

checkpoint_timeout

Parameter description: Specifies the maximum time between automatic WAL checkpoints.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 30 to 3600. The unit is second.

If the value of checkpoint_segments is increased, you need to increase the value of this parameter. The increase of these two parameters further requires the increase of shared_buffers. Consider all these parameters during setting.

Default value: 15min

checkpoint_completion_target

Parameter description: Specifies the completion target of each checkpoint, as a fraction of total time between checkpoints.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: a floating point number ranging from 0.0 to 1.0

Default value: 0.5

NOTE: 0.5 indicates that each checkpoint should be complete within 50% of the interval between checkpoints.

checkpoint_warning

Parameter description: Specifies a time in seconds. If the checkpoint interval is close to this time due to filling of checkpoint segment files, a message is sent to the server log to suggest an increase in the checkpoint_segments value.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 0 to INT_MAX. The unit is second. 0 indicates that the warning is disabled.

Default value: 5min

Recommended value:5min

checkpoint_wait_timeout

Parameter description: Sets the longest time that the checkpoint waits for the checkpointer thread to start.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 2 to 3600. The unit is second.

Default value: 1min

enable_incremental_checkpoint

Parameter description: Specifies whether to enable incremental checkpointing.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

Default value: on

enable_double_write

Parameter description: Specifies whether to enable the doublewrite buffer. When the incremental checkpointing is enabled, enable_double_write is enabled at the same time and the doublewrite buffer instead of full_page_writes is used to prevent partial page writes.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

Default value: on

incremental_checkpoint_timeout

Parameter description: Specifies the maximum interval between automatic WAL checkpoints when the incremental checkpointing is enabled.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 1 to 3600. The unit is second.

Default value: 1min

enable_xlog_prune

Parameter description: Specifies whether the primary server reclaims logs when any standby server is disconnected.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• When set to on, the host will not reclaim logs when any of the standby machines is disconnected.
• When set to off, the host will reclaim the log when any of the standby machines is disconnected.

Default value: on

max_redo_log_size

Parameter description: Specifies the size of logs before the recovery point and the current log location. You are advised not to set this parameter to a large value if the RTO is concerned.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 163840 to 2147483647. The unit is KB.

Default value: 1GB

max_size_for_xlog_prune

Parameter description: It takes effect when enable_xlog_prune is turned on. If the backup machine is disconnected and the xlog log size is greater than this threshold, the log will be recycled.

This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: integer, 0～2147483647, the unit is KB

Default value: 2147483647,in KB