November 23, 2014

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. Yuriy Vidineev says:

    Will this release be available in percona debain apt repository (

  2. Chris says:

    Only version 5.5.13-rel20.4-136.maverick is still available from the Maverick APT Repository.

  3. Yugene says:

    Waiting for 5.5.15 (or at least 5.5.14) in APT Squeeze repository, cause 5.5.13 which is currently latest available seems to have a bug in replication (described it at

  4. Rodrigo Gadea says:

    A last-minute bug on our apt repositories delayed the availability of the packages. It was fixed and all packages are available now in the repositories:

    Sorry for the inconvenience

  5. 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?

  6. 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.

  7. Cédric says:


    Does the improved memory engine works with internal temporary tables ?


  8. Cédric,

    It does not work with internal tables right now, but we may do it in future.

  9. Cédric says:

    Thank you Vadim for the reply. I’ve understood since I read the doc :-)

  10. Hi Laurynas, Vadim,
    Regarding the use of MEMORY engine for temp table handling when TEXT/BLOG is present. Was this problem solved?


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