Undo
undo_space_limit_size
Parameter description: Specifies the threshold for forcibly recycling undo space. When the undo space usage reaches 80% of the threshold, forcible recycling starts. You can set this parameter to a large value based on service requirements and then set it to a proper value based on the actual undo space usage. The value of undo_space_limit_size must be equal to or greater than that of undo_limit_size_per_transaction.
This is a SIGHUP parameter. Set it based on instructions in Table 1.
Value range: an integer ranging from 102400 to 2147483647. The unit is 8 KB.
Default value: 256GB
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. You are advised to set undo_limit_size_per_transaction to a value less than or equal to that of undo_space_limit_size. If the value of undo_limit_size_per_transaction is greater than that of undo_space_limit_size, the displayed value is the same as the configured value when you run the show undo_limit_size_per_transaction command to query the parameter. The only difference is that the smaller value between undo_space_limit_size and undo_limit_size_per_transaction is used as the actual undo space threshold of a single transaction. If the undo_limit_size_per_transaction is set to a value greater than 1 TB, the system performance and stability may be affected.
This is a SIGHUP parameter. Set it based on instructions in Table 1.
Value range: an integer ranging from 256 to 2147483647. The unit is 8 KB.
Default value: 32 GB
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