Settings

synchronous_commit

Parameter description: Specifies the synchronization mode of the current transaction.

Type: USERSET

Value range: enumerated values

• on indicates synchronization logs of a standby server are flushed to disks.
• off indicates asynchronous commit.
• local indicates local commit.
• remote_write indicates synchronization logs of a standby server are written to disks.
• remote_receive indicates synchronization logs of a standby server are required to receive data.

Default value: on

commit_delay

Parameter description: Specifies the duration of committed data be stored in the WAL buffer.

Type: USERSET

Value range: an integer, ranging from 0 to 100000 (unit: μs). 0 indicates no delay.

Default value: 0

• When this parameter is set to a value other than 0, the committed transaction is stored in the WAL buffer instead of being written to the WAL immediately. Then, the WalWriter process flushes the buffer out to disks periodically.
• If system load is high, other transactions are probably ready to be committed within the delay. If no transactions are waiting to be submitted, the delay is a waste of time.

commit_siblings

Parameter description: Specifies a limit on the number of ongoing transactions. If the number of ongoing transactions is greater than the limit, a new transaction will wait for the period of time specified by commit_delay before it is submitted. If the number of ongoing transactions is less than the limit, the new transaction is immediately written into a WAL.

Type: USERSET

Value range: an integer ranging from 0 to 1000

Default value: 5

enable_xlog_group_insert

Parameter description: Specifies whether to enable the group insertion mode for WALs. Only the Kunpeng architecture supports this parameter.

Type: SIGHUP

Value range: Boolean

• on: enabled
• off: disabled

Default value: on

wal_compression

Parameter description: Specifies whether to compress FPI pages.

Type: USERSET

Value range: Boolean

• on: enable the compression
• off: disable the compression

Default value: on

• Only zlib compression algorithm is supported.
• For clusters that are upgraded to the current version from an earlier version, this parameter is set to off by default. You can run the gs_guc command to enable the FPI compression function if needed.
• If the current version is a newly installed version, this parameter is set to on by default.
• If this parameter is manually enabled for a cluster upgraded from an earlier version, the cluster cannot be rolled back.

wal_compression_level

Parameter description: Specifies the compression level of zlib compression algorithm when the wal_compression parameter is enabled.

Type: USERSET

Value range: an integer ranging from 0 to 9.

• 0 indicates no compression.
• 1 indicates the lowest compression ratio.
• 9 indicates the highest compression ratio.

Default value: 9