MySQL 5.5.39 发布，此版本是 MySQL 5.5 的最新版本，是个稳定版本。
此版本跟上一版本一样，并没有太大改进，包括了 2 个功能改进和 24 个 bug 修复。
支持 CMake 3
弃用了 timed_mutexes 系统变量
InnoDB: Opening a parent table that has thousands of child tables could result in a long semaphore wait condition.
Partitioning: Selecting from a table having multiple columns in its primary key and partitioned by LIST COLUMNS(R), where R was the last (rightmost) column listed in the primary key definition, returned an incorrect result. (Bug #71095)
Replication: When using row-based replication, updating or deleting a row on the master that did not exist on the slave led to failure of the slave when it tried to process the change. This problem occurred with InnoDB tables lacking a primary key. (Bug #72085)
Replication: A group of threads involved in acquiring locks could deadlock in a certain scenario. (Bug #69954)
ALTER TABLE on a partitioned table could result in the wrong storage engine being written into the table’s .frm file and displayed in SHOW CREATE TABLE.
InnoDB temporary files could be used to mount a code-execution attack.
An assertion could be raised when creating a index on a prefix of a TINYBLOB or GEOMETRY column in an InnoDB column.
Deadlock could occur if three threads simultaneously performed INSTALL PLUGIN, SHOW VARIABLES, and mysql_change_user(). (Bug #71236, Bug #72870)
MySQL did not compile with Bison 3. A workaround is to downgrade to Bison 2. (Bug #71250)