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InnoDB 1.1 for MySQL 5.5 User's Guide
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7.21. Improved Log Sys Mutex

This is another performance improvement that comes for free, with no user action or configuration needed. The details here are intended for performance experts who delve into the InnoDB source code, or interpret reports with keywords such as mutex and log_sys.

The mutex known as the log sys mutex has historically done double duty, controlling access to internal data structures related to log records and the LSN, as well as pages in the buffer pool that are changed when a mini-transaction is committed. Starting in InnoDB 1.1 with MySQL 5.5, these two kinds of operations are protected by separate mutexes, with a new log_buf mutex controlling writes to buffer pool pages due to mini-transactions.

For performance considerations for InnoDB locking operations, see Optimizing Locking Operations.

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