Percona Server 5.5.15-21.0


Percona is glad to announce the release of Percona Server 5.5.15-21.0 on August 31, 2011 (Downloads are available here and from the Percona Software Repositories).

Based on MySQL 5.5.15, including all the bug fixes in it, Percona Server 5.5.15-21.0 is now the current stable release in the 5.5 series. All of Percona’s software is open-source and free, all the details of the release can be found in the 5.5.15-21.0 milestone at Launchpad.


Improved MEMORY Storage Engine

As of MySQL 5.5.15, a Fixed Row Format (FRF) is still being used in the MEMORY storage engine. The fixed row format imposes restrictions on the type of columns as it assigns on advance a limited amount of memory per row. This renders a VARCHAR field in a CHAR field in practice, making impossible to have a TEXT or BLOB field with that engine implementation.

To overcome this limitation, the Improved MEMORY Storage Engine is introduced in this release for supporting true VARCHARVARBINARYTEXT and BLOB fields in MEMORY tables.

This implementation is based on the Dynamic Row Format (DFR) introduced by the mysql-heap-dynamic-rows patch.

DFR is used to store column values in a variable-length form, thus helping to decrease memory footprint of those columns and making possible BLOB and TEXT fields and real VARCHAR and VARBINARY.

For performance reasons, a mixed solution is implemented: the fixed format is used at the beginning of the row, while the dynamic one is used for the rest of it. All values for columns used in indexes are stored in fixed format at the first block of the row, then the following columns are handled with DRF.

More information about the usage and implementation of the Improved MEMORY Storage Engine can be found in its documentation.

More Information




  1. Steve Jackson says

    In relation to the memory storage engine improvements. I find nothing in the documentation for this patch regarding usage in temp tables… will this feature have any effect on size/performance of memory temp tables?

  2. Laurynas Biveinis says

    Steve –

    The current release changes nothing with respect to temp table handling (i.e. MyISAM is still used even if MEMORY could be used now). We are working on this, but no ETA.

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