Flashback

This section describes parameters related to the flashback function. In this version, only the Ustore engine supports flashback, while the Astore engine does not support flashback.

enable_recyclebin

Parameter description: Specifies whether the recycle bin is enabled or disabled in real time.

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

Value range: Boolean

Default value: off

recyclebin_retention_time

Parameter description: Specifies the retention period of objects in the recycle bin. The objects will be automatically deleted after the retention period expires.

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

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

Default value: 15 min (900s)

version_retention_age

Parameter description: Specifies the number of transactions retained in the old version. If the number of transactions exceeds the value of this parameter, the old version will be recycled and cleared.

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

Value range: an integer ranging from 0 to 576460752303423487. 0 means no delay.

Default value: 0

This parameter has been deprecated.

vacuum_defer_cleanup_age

Parameter description: Specifies the number of transactions by which VACUUM will defer the cleanup of invalid row-store table records, so that VACUUM and VACUUM FULL do not clean up deleted tuples immediately. You can also set this parameter to configure the retention period of the flashback function in the old version.

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

Value range: an integer ranging from 0 to 1000000. 0 means no delay. The value range needs to be extended to 100 million.

Default value: 0

This parameter can be ignored when you use the Ustore engine to flash back. It serves the Astore flashback function of the earlier version and has other functions. The flashback function is not used in this version.

undo_retention_time

Parameter description: Specifies the period for retaining undo logs of earlier versions.

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

Value range: an integer ranging from 0 to 259200. The unit is second.

Default value: 0

If this parameter is set to 0 during the Ustore flashback query, the snapshot information at the flashback point will be cleared. In earlier versions, no flashback query can be performed. When a flashback query is performed, the error message "cannot find the restore point" is displayed.
If the time within which the undo logs of earlier versions need to be retained is time1 and the SQL statement execution time for the flashback query is time2, you need to set undo_retention_time to a value greater than time1 + time2. That is, set undo_retention_time to a value greater than time1 + time2 + 3s. You are advised to set undo_retention_time to a value equal to time1 + 1.5 x time2. For example, if you want to retain the logs of earlier versions within the latest 3 hours, and the SQL statement execution time for the flashback query is 1 hour, set undo_retention_time to a value equal to 3 hours + 1.5 x 1 hour, that is, 4.5 hours.