Undo

undo_space_limit_size

Parameter description: Specifies the undo forcible reclamation threshold. If 80% of the threshold is reached, forcible reclamation is triggered.

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

Value range: an integer ranging from 800 MB to 32 TB

Default value: 32 GB

undo_limit_size_per_transaction

Parameter description: Specifies the undo space threshold of a single transaction. If the threshold is reached, the transaction is rolled back due to an error.

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

Value range: an integer ranging from 100 MB to 32 TB

Default value: 32 GB

undo_zone_count

Parameter description: Specifies the number of undo zones that can be allocated in the memory. If the number reaches the threshold or the value set this time is less than the value set last time, an error is reported. After a proper value is set based on the rule, the number of undo zones becomes normal. If this parameter is set to 0, the undo function is disabled and Ustore tables cannot be created.

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

Value range: an integer ranging from 0 to 1048576

Value constraint:

1. The value set this time must be greater than or equal to the value set last time. If the value is incorrect, the database cannot be restored. You need to reset the value and restart the database to restore the database.
2. The value of undo_zone_count needs to be adjusted based on the value of max_connections. After changing the value of max_connections, you need to change the value of undo_zone_count, which must be four times that of max_connections.

Default value: 0