Dear MySQL users,

MySQL 5.5.20 is a new version of the 5.5 production release of the
world's most popular open source database. MySQL 5.5.20 is recommended
for use on production systems.

MySQL 5.5 includes several high-impact enhancements to improve the
performance and scalability of the MySQL Database, taking advantage of
the latest multi-CPU and multi-core hardware and operating systems. In
addition, with release 5.5, InnoDB is now the default storage engine for
the MySQL Database, delivering ACID transactions, referential integrity
and crash recovery by default.

MySQL 5.5 also provides a number of additional enhancements including:

- Significantly improved performance on Windows, with various
Windows specific features and improvements
- Higher availability, with new semi-synchronous replication and
Replication Heart Beat
- Improved usability, with Improved index and table partitioning,
SIGNAL/RESIGNAL support and enhanced diagnostics, including a new
Performance Schema monitoring capability.

For a more complete look at what's new in MySQL 5.5, please see the
following resources:

MySQL 5.5 is GA, Interview with Tomas Ulin:
http://dev.mysql.com/tech-resources/interviews/thomas-ulin-mysql-55.html

Documentation:
http://dev.mysql.com/doc/refman/5.5/en/mysql-nutshell.html

Whitepaper: What's New in MySQL 5.5:
http://dev.mysql.com/why-mysql/white-papers/mysql-wp-whatsnew-mysql-55.php

If you are running a MySQL production level system, we would like to
direct your attention to MySQL Enterprise Edition, which includes the
most comprehensive set of MySQL production, backup, monitoring,
modeling, development, and administration tools so businesses can
achieve the highest levels of MySQL performance, security and uptime.
http://mysql.com/products/enterprise/

For information on installing MySQL 5.5.20 on new servers, please see
the MySQL installation documentation at
http://dev.mysql.com/doc/refman/5.5/en/installing.html

For upgrading from previous MySQL releases, please see the important
upgrade considerations at:
http://dev.mysql.com/doc/refman/5.5/en/upgrading.html

MySQL Database 5.5.20 is available in source and binary form for a
number of platforms from our download pages at:
http://dev.mysql.com/downloads/mysql/

Not all mirror sites may be up to date at this point in time, so if you
can't find this version on some mirror, please try again later or choose
another download site.

We welcome and appreciate your feedback, bug reports, bug fixes,
patches, etc.:
http://forge.mysql.com/wiki/Contributing

The following section lists the changes in the MySQL source code since
the previous released version of MySQL 5.5. It may also be viewed
online at:
http://dev.mysql.com/doc/refman/5.5/en/news-5-5-20.html

Enjoy!


D.1.1. Changes in MySQL 5.5.20 (10 January 2011)

Functionality Added or Changed

* A new server option, --slow-start-timeout, controls the
Windows service control manager's service start timeout. The
value is the maximum number of milliseconds that the service
control manager waits before trying to kill the MySQL service
during startup. The default value is 15000 (15 seconds). If
the MySQL service takes too long to start, you may need to
increase this value. A value of 0 means there is no timeout.
(Bug #45546, Bug #11754011)

Bugs Fixed

* Important Change: Replication: Setting an empty user in a
CHANGE MASTER TO statement caused an invalid internal result
and is no longer permitted. Trying to use MASTER_USER='' or
setting MASTER_PASSWORD while leaving MASTER_USER unset causes
the statement to fail with an error. (Bug #13427949)

* Important Change: Replication: Moving the binary log file,
relay log file, or both files to a new location, then
restarting the server with a new value for --log-bin,
--relay-log, or both, caused the server to abort on start.
This was because the entries in the index file overrode the
new location. In addition, paths were calculated relative to
datadir (rather than to the --log-bin or --relay-log values).
The fix for this problem means that, when the server reads an
entry from the index file, it now checks whether the entry
contains a relative path. If it does, the relative part of the
path is replaced with the absolute path set using the
--log-bin or --relay-log option. An absolute path remains
unchanged; in such a case, the index must be edited manually
to enable the new path or paths to be used. (Bug #11745230,
Bug #12133)

* InnoDB Storage Engine: When doing a live downgrade from MySQL
5.6.4 or later, with innodb_page_size
(http://dev.mysql.com/doc/refman/5.6/en/innodb-parameters.html
#sysvar_innodb_page_size) set to a value other than 16384, now
the earlier MySQL version reports that the page size is
incompatible with the older version, rather than crashing or
displaying a "corruption" error. (Bug #13116225)

* InnoDB Storage Engine: Issuing INSERT...ON DUPLICATE KEY
statements for InnoDB tables from concurrent threads could
cause a deadlock
(http://dev.mysql.com/doc/refman/5.5/en/glossary.html#glos_dea
dlock), particularly with the INSERT...ON DUPLICATE KEY UPDATE
form. The fix avoids deadlocks caused by the same row being
accessed by more than one transaction. Deadlocks could still
occur when multiple rows are inserted and updated
simultaneously by different transactions in inconsistent
order; those types of deadlocks require the standard error
handling on the application side, of re-trying the
transaction. (Bug #11759688, Bug #52020)

* An incorrect InnoDB assertion could cause the server to halt.
This issue only affected debug builds. The assertion
referenced the source file btr0pcur.ic and the variable
cursor->pos_state. (Bug #13358468)

* Locale information for FORMAT() function instances was lost in
view definitions. (Bug #63020, Bug #13344643)

* The handle_segfault() signal-handler code in mysqld could
itself crash due to calling unsafe functions. (Bug #54082, Bug
#11761576)

* Enabling myisam_use_mmap could cause the server to crash. (Bug
#48726, Bug #11756764)

* Concurrent access to ARCHIVE tables could cause corruption.
(Bug #42784, Bug #11751793)


On behalf of the MySQL Build Team,
Joerg Bruehe/Hery Ramilison

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