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14.2.6 InnoDB Temporary Table Undo Logs

MySQL 5.7.2 introduces a new type of undo log for both normal and compressed temporary tables and related objects. The new type of undo log is not a redo log, as temporary tables are not recovered during crash recovery and do not require redo logs. Temporary table undo logs are, however, required for rollback, MVCC, and purging while the server is running. This special type of non-redo undo log benefits performance by avoiding redo logging I/O for temporary tables and related objects. The new undo log resides in the temporary tablespace. The default temporary tablespace file, ibtmp1, is located in the data directory by default and is always recreated on server startup. A user defined location for the temporary tablespace file can be specified by setting innodb_temp_data_file_path.

With this change, 32 rollback segments are now reserved for temporary table undo logs for transactions that modify temporary tables and related objects. This reduces the maximum number of rollback segments available for data-modifying transactions that generate undo records from 128 to 96, which reduces the limit on concurrent data-modifying transactions from 128K to 96K. For more information see Section 14.2.3, “InnoDB Multi-Versioning” and Section 14.5.7, “Limits on InnoDB Tables”.

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