オリジナル版：http://dev.mysql.com/doc/refman/5.5/en/news-5-5-21.html
MySQL 5.5.21は世界でもっともポピュラーなオープンソースデータベースの5.5のプロダクトリリースの新しいバージョンです。MySQL 5.5.21はプロダクションシステムでの使用をお勧めします。
MySQL 5.5は最新のマルチCPUやマルチコアハードウェアやオペレーティングシステムの利点を生かし、MySQLデータベースのパフォーマンスとスケーラビリ ティを改善するための影響の大きい変更をいくつか含んでいます。現在ではInnoDBがMySQLデータベースのデフォルトのストレージエンジンであり、 ACIDトランザクション、参照整合性、クラッシュリカバリをデフォルトで提供しています。
MySQL 5.5は以下の多くの新しい強化も含んでいます：
- Windowsにおける特有の機能と改善を利用した著しいパフォーマンス向上 - 新しい準同期レプリケーションとレプリケーションハートビートによるより高いレベルの可用性 - 改善されたインデックスとテーブルパーティショニング、SIGNAL/RESIGNALサポート、そして新しいPERFORMANCE_SCHEMAに含まれる強化された診断法による改善されたユーザビリティ
MySQL 5.5の新機能のより完全な概観については、以下のリソースを参照下さい。
MySQL 5.5 GA、Tomas Ulinのインタビュー:
http://dev.mysql.com/tech-resources/interviews/thomas-ulin-mysql-55.html
ドキュメント:
http://dev.mysql.com/doc/refman/5.5/en/mysql-nutshell.html
ホワイトペーパー: MySQL 5.5の新機能
http://dev.mysql.com/doc/refman/5.5/en/mysql-nutshell.html
製品レベルのシステムでMySQLを稼動させているならば、MySQL製品、バックアップ、モニタリング、モデリング、開発、管理ツールの包括的なセット を含むMySQLパフォーマンス、セキュリティ、アップタイムの高いレベルを実現するMySQL Enterprise Editionの製品詳細に注目してください。
http://mysql.com/products/enterprise/
新しいサーバへMySQL 5.5.21をインストールする情報として、以下のMySQLのインストールドキュメントを参照してください。
http://dev.mysql.com/doc/refman/5.5/en/installing.html
前回のMySQLリリースからアップグレードするには、以下のアップグレードについての注意事項を参照してください。
http://dev.mysql.com/doc/refman/5.5/en/upgrading-from-previous-series.html
MySQL Server 5.5は、http://dev.mysql.com/downloads/とミラーサイトのダウンロード・ページから、ソースコード及び多くのプラットフォームのためのバイナリで現在利用可能です。
すべてのミラーサイトが現在、最新であるとは限らないことに注意してください。
あるミラーサイトでこのバージョンを見つけることができない場合は、再度確認を行うか、あるいは別のダウンロード・サイトを選択してください。
バグレポート、バグ修正、パッチ等の情報をお待ちしております。
http://forge.mysql.com/wiki/Contributing
次の節では、MySQL 5.5の以前のバージョンからのMySQLソースコードの変更を記載しています。これはオンラインでも閲覧できます。
http://dev.mysql.com/doc/refman/5.5/en/news-5-5-21.html
Changes in MySQL 5.5.21 (17 February 2012)
Functionality Added or Changed
* A new CMake option, MYSQL_PROJECT_NAME, can be set on Windows
or Mac OS X to be used in the project name. (Bug #13551687)
Bugs Fixed
* Performance: InnoDB Storage Engine: Memory allocation for
InnoDB tables was reorganized to reduce the memory overhead
for large numbers of tables or partitions, avoiding situations
where the "resident set size" could grow regardless of FLUSH
TABLES statements. The problem was most evident for tables
with large row size. Some of the memory that was formerly
allocated for every open table is now allocated only when the
table is modified for the first time. (Bug #11764622, Bug
#57480)
* Incompatible Change: An earlier change (in MySQL 5.1.59 and
5.5.16) was found to modify date-handling behavior in General
Availability-status series (MySQL 5.1 and 5.5). This change
has been reverted.
The change was that several functions became more strict when
passed a DATE() function value as their argument, thus they
rejected incomplete dates with a day part of zero. These
functions were affected: CONVERT_TZ(), DATE_ADD(), DATE_SUB(),
DAYOFYEAR(), LAST_DAY(), TIMESTAMPDIFF(), TO_DAYS(),
TO_SECONDS(), WEEK(), WEEKDAY(), WEEKOFYEAR(), YEARWEEK(). The
previous behavior has been restored. (Bug #13458237)
* InnoDB Storage Engine: A Valgrind error was fixed in the
function os_aio_init(). (Bug #13612811)
* InnoDB Storage Engine: The server could crash when creating an
InnoDB temporary table under Linux, if the $TMPDIR setting
points to a tmpfs filesystem and innodb_use_native_aio is
enabled, as it is by default in MySQL 5.5.4 and higher. The
entry in the error log looked like:
101123 2:10:59 InnoDB: Operating system error number
22 in a file operation.
InnoDB: Error number 22 means 'Invalid argument'.
The crash occurred because asynchronous I/O is not supported
on tmpfs in some Linux kernel versions. The workaround was to
turn off the innodb_use_native_aio setting or use a different
temporary directory. The fix causes InnoDB to turn off the
innodb_use_native_aio setting automatically if it detects that
the temporary file directory does not support asynchronous
I/O. (Bug #13593888, Bug #11765450, Bug #58421)
* InnoDB Storage Engine: References to C preprocessor symbols
and macros HAVE_purify, UNIV_INIT_MEM_TO_ZERO, and
UNIV_SET_MEM_TO_ZERO were removed from the InnoDB source code.
They were only used in debug builds instrumented for Valgrind.
They are replaced by calls to the UNIV_MEM_INVALID() macro.
(Bug #13418934)
* InnoDB Storage Engine: The MySQL server could halt with an
assertion error:
InnoDB: Failing assertion: page_get_n_recs(page) > 1
Subsequent restarts could fail with the same error. The error
occurred during a purge
(http://dev.mysql.com/doc/refman/5.5/en/glossary.html#glos_pur
ge) operation involving the InnoDB change buffer
(http://dev.mysql.com/doc/refman/5.5/en/glossary.html#glos_cha
nge_buffer). The workaround was to set the configuration
option innodb_change_buffering=inserts. (Bug #13413535, Bug
#61104)
* InnoDB Storage Engine: With 1024 InnoDB transactions running
concurrently and the innodb_file_per_table setting enabled,
a CREATE TABLE operation for an InnoDB table could fail. The
.ibd file from the failed CREATE TABLE was left behind,
preventing the table from being created later, after the load
had dropped.
The fix adds error handling to delete the erroneous .ibd file.
This error was less likely to occur in MySQL 5.5 and 5.6,
because raising the number of InnoDB undo slots increased the
number of simultaneous transactions needed to trigger the bug,
from 1K to 128K. (Bug #12400341)
* Replication: Executing mysqlbinlog with the --start-position=N
option, where N was equal either to 0 or to a value greater
than the length of the dump file, caused it to crash.
This issue was introduced in MySQL 5.5.18 by the fix for Bug
#32228 and Bug #11747416. (Bug #13593869, Bug #64035)
* Replication: On Windows replication slave hosts, STOP SLAVE
took an excessive length of time to complete when the master
was down. (Bug #11752315, Bug #43460)
* A query that used an index on a CHAR column referenced in a
BETWEEN clause could return invalid results. (Bug #13463488,
Bug #63437)
* Expressions that compared a BIGINT column with any non-integer
constant were performed using integers rather than decimal or
float values, with the result that the constant could be
truncated. This could lead to any such comparison that used <,
>, <=, >=, =, !=/<>, IN, or BETWEEN yielding false positive or
negative results. (Bug #13463415, Bug #11758543, Bug #63502,
Bug #50756)
* When the optimizer performed conversion of DECIMAL values
while evaluating range conditions, it could produce incorrect
results. (Bug #13453382)
* When running mysqldump with both the --single-transaction and
--flush-logs options, the flushing of the log performed an
implicit COMMIT (see Section 12.3.3, "Statements That Cause an
Implicit Commit"), causing more than one transaction to be
used and thus breaking consistency. (Bug #12809202, Bug
#61854)
* It was possible in the event of successive failures for
mysqld_safe to restart quickly enough to consume excessive
amounts of CPU. Now, on systems that support the sleep and
date system utilities, mysqld_safe checks to see whether it
has restarted more than 5 times in the current second, and if
so, waits 1 second before attempting another restart. (Bug
#11761530, Bug #54035)
* When used with the --xml option, mysqldump --routines failed
to dump any stored routines, triggers, or events. (Bug
#11760384, Bug #52792)
* It was possible on replication slaves where FEDERATED tables
were in use to get timeouts on long-running operations, such
as Error 1160 Got an error writing communication packets. The
FEDERATED tables did not need to be replicated for the issue
to occur. (Bug #11758931, Bug #51196)
References: See also Bug #12896628, Bug #61790.
* If an attempt to initiate a statement failed, the issue could
not be reported to the client because it was not prepared to
receive any error messages prior to the execution of any
statement. Since the user could not execute any queries, they
were simply disconnected without providing a clear error.
After the fix for this issue, the client is prepared for an
error as soon as it attempts to initiate a statement, so that
the error can be reported prior to disconnecting the user.
(Bug #11755281, Bug #47032)
* Using myisamchk with the sort recover method to repair a table
having fixed-width row format could cause the row pointer size
to be reduced, effectively resulting in a smaller maximum data
file size. (Bug #48848, Bug #11756869)
* On Windows, the server incorrectly constructed the full path
name of the plugin binary for INSTALL PLUGIN and CREATE
FUNCTION ... SONAME. (Bug #45549, Bug #11754014)
* The stored routine cache was subject to a small memory leak
that over time or with many routines being used could result
in out-of-memory errors. (Bug #44585, Bug #11753187)