Starting in InnoDB 1.1 with MySQL 5.5, the purge operations (a type of garbage collection) that InnoDB performs automatically can be done in a separate thread, rather than as part of the master thread. This change improves scalability, because the main database operations run independently from maintenance work happening in the background.
To enable this feature, set the configuration option
1, as opposed to the default of 0, which
combines the purge operation into the master thread.
You might not notice a significant speedup, because the purge
thread might encounter new types of contention; the single purge
thread really lays the groundwork for further tuning and possibly
multiple purge threads in the future. There is another new
innodb_purge_batch_size with a
default of 20 and maximum of 5000. This option is mainly intended
for experimentation and tuning of purge operations, and should not
be interesting to typical users.
For more information about InnoDB I/O performance, see
Section 8.5.7, “Optimizing
InnoDB Disk I/O”.