Temporary table undo logs are used for temporary tables and
related objects. This 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, used for rollback 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. Temporary table undo logs reside 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
32 rollback segments are reserved for temporary table undo logs for transactions that modify temporary tables and related objects, which means that the maximum number of rollback segments available for data-modifying transactions that generate undo records is 96. With 96 available rollback segments, the limit on concurrent data-modifying transactions is 96K. For more information see Section 15.3, “InnoDB Multi-Versioning” and Section 15.8.8, “Limits on InnoDB Tables”.