MySQL5.5.19发布，新增3个主要功能，修复6处BUG_MySQL

MYSQL多用于网站制作中的数据库。与PHP,APACHE。构成LMAP架构。

本文转载自:http://www.mwinds.net/read.php?lmid=30&id=714

新增功能

• 通过为元数据锁对象创建缓存，提升了Windows XP系统中元数据锁操作的性能，这可以使服务器避免在XP中创建和销毁同步对象的高成本操作。
• 增加了一个新的系统变量metadata_locks_cache_size，允许控制缓存大小，默认大小为1024。
• 复制：在此之前，主从服务器通过使用非本地认证的主账户进行复制连接。现在也适用于Windows本地认证。

• InnoDB存储引擎：当DML操作的缓冲做了大量改变时，尤其是使用DELETE语句时，可能造成服务器死锁。
• DBL_MAX返回DBL_MAX，而不是“inf”。
• 当使用--write-binlog或--skip-write-binlog选项运行时，mysql_upgrade不升级系统表或创建mysql_upgrade_info文件。
• 如果一个插件被卸载，使用PLUGIN_VAR_MEMALLOC标记的字符串类型变量的局部变量不被释放。

?InnoDB Storage Engine: An internal deadlock could occur within InnoDB, on a server doing a substantial amount of change buffering for DML operations, particularly DELETE statements. (Bug #13340047)
?InnoDB Storage Engine: (Bug #12884631, Bug #62146)
?Rounding DBL_MAX returned DBL_MAX, not 'inf'. (Bug #13261955)
?mysql_upgrade did not upgrade the system tables or create the mysql_upgrade_info file when run with the --write-binlog or --skip-write-binlog option. (Bug #60223, Bug #11827359)
?If a plugin was uninstalled, thread local variables for plugin variables of string type with wth PLUGIN_VAR_MEMALLOC flag were not freed. (Bug #56652, Bug #11763882)
?Deadlock could occur when these four things happened at the same time: 1) An old dump thread was waiting for the binary log to grow. 2) The slave server that replicates from the old dump thread tried to reconnect. During reconnection, the new dump thread tried to kill the old dump thread. 3) A KILL statement tried to kill the old dump thread. 4) An INSERT statement caused a binary log rotation. (Bug #56299, Bug #11763573)