Key-Value Locking

To increase concurrency, the database server supports key-value locking in the B-tree index. Key-value locking locks only the value of the key instead of the physical location in the B-tree index.

One of the most important uses for key-value locking is to assure that a unique key remains unique through the end of the transaction that deleted it. Without this protection mechanism, user A might delete a unique key within a transaction, and user B might insert a row with the same key before the transaction commits. This scenario makes rollback by user A impossible. Key-value locking prevents user B from inserting the row until the end of user A's transaction.

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