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Designing JDBC Applications for Performance Optimization : Managing Connections and Updates : Managing Commits in Transactions

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Managing Commits in Transactions

Committing transactions is slow because of the amount of disk I/O and potentially network round trips that are required. Always turn off Autocommit by using Connection.setAutoCommit(false).
What does a commit actually involve? The database server must flush back to disk every data page that contains updated or new data. This is usually a sequential write to a journal file, but nevertheless, it involves disk I/O. By default, Autocommit is on when connecting to a data source, and Autocommit mode usually impairs performance because of the significant amount of disk I/O needed to commit every operation.
Furthermore, most database servers do not provide a native Autocommit mode. For this type of server, the JDBC driver must explicitly issue a COMMIT statement and a BEGIN TRANSACTION for every operation sent to the server. In addition to the large amount of disk I/O required to support Autocommit mode, a performance penalty is paid for up to three network requests for every statement issued by an application.
Although using transactions can help application performance, do not take this tip too far. Leaving transactions active can reduce throughput by holding locks on rows for longer than necessary, preventing other users from accessing the rows. Commit transactions in intervals that allow maximum concurrency.