Concurrency erro when deleteing or updating multiple key field


03-Apr-2020 13:15

Alice’s UPDATE is blocked until Bob releases the write locks at the end of his current transaction.But Alice’s persistence context is using a stale entity snapshot, so she overwrites Bob changes, leading to another lost update situation.Choosing the isolation level is about finding the right balance of consistency and scalability for our current application requirements.All the following examples are going to be run on Postgre SQL 9.3.Both transactions should use the FOR UPDATE locking.If the first transaction doesn’t acquire the write locks, the lost update can still happen.If two transactions attempt to modify the same record, the second transaction will wait for the first one to either commit or rollback.

concurrency erro when deleteing or updating multiple key field-38

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If two transactions try to update the same row, the second transaction must wait for the first one to either commit or rollback, and if the first transaction has been committed, then the second transaction DML WHERE clause must be reevaluated to see if the match is still relevant.

Another solution would be to use the FOR UPDATE with the default Read Committed isolation level.

This locking clause acquires the same write locks as with UPDATE and DELETE statements.

Follow @vlad_mihalcea A database is highly concurrent system.

There’s always a chance of update conflicts, like when two concurring transactions try to update the same record.

The SQL standard defines three consistency anomalies (phenomena): anomaly and that’s what we are going to discuss in this current article.



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