How does oracle speed up the rollback

This article will explain in detail how oracle speeds up rollback. Xiaobian thinks it is quite practical, so share it with you for reference. I hope you can gain something after reading this article.

I remember when a large number of data were deleted, the rollback segment was full, resulting in the failure of the delete operation, a large number of transactions were rolled back, and this table was used by transactions. During rollback, the cpu idle dropped sharply, the cpu and io were busy, and the transaction could not use this table at all. The program directly hung up. It was a bloody lesson. As a dba, I was trying to speed up the rollback:

Increase the number of parallel rollback processes, set to HIGH rollback processes =4*CPU count. Executing in sql command line mode

dynamic modification

ALTER SYSTEM SET FAST_START_PARALLEL_ROLLBACK = HIGH;

Parameter explanation:

Values:

FALSE

Parallel rollback is disabled

LOW

Limits the maximum degree of parallelism to 2 * CPU_COUNT

HIGH

Limits the maximum degree of parallelism to 4 * CPU_COUNT

If you change the value of this parameter, then transaction recovery will be stopped and restarted with t

Related Views:

select * from v$fast_start_transactions

During rollback, the progress of rollback can be determined by viewing V$FAST_START_TRANSACTIONS

USN: undo segment corresponding to transaction

STATE: The state of the transaction, optionally (BE RECOVERED, RECOVERED, or RECOVERING)

UNDOBLOCKSDONE: Completed undo block

UNDOBLOCKSTOTAL: Total undo data block

CPUTIME: Time that has been rolled back in seconds

RCVSERVERS: Number of parallel processes rolled back

After the rollback ends, fast_start_parallel_rollback returns to false to reduce the impact of undo.

alter system set fast_start_parallel_rollback= FALSE;

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