Incompatible Change: InnoDB rolls back only the last statement on a transaction timeout. A new option, --innodb_rollback_on_timeout, causes InnoDB to abort and roll back the entire transaction if a transaction timeout occurs (the same behavior as in MySQL 5.0.13 and earlier). (Bug#24200)

Performance: Evaluation of subqueries that require the filesort algorithm were allocating and freeing the sort_buffer_size buffer many times, resulting in slow performance. Now the buffer is allocated once and reused. (Bug#21727)

Replication: A stored procedure, executed from a connection using a binary character set, and which wrote multibyte data, would write incorrectly escaped entries to the binary log. This caused syntax errors, and caused replication to fail. (Bug#23619, Bug#24492)

The loose index scan optimization for GROUP BY with MIN or MAX was not applied within other queries, such as CREATE TABLE ... SELECT ..., INSERT ... SELECT ..., or in the FROM clauses of subqueries. (Bug#24156)

The size of MEMORY tables and internal temporary tables was limited to 4GB on 64-bit Windows systems. (Bug#24052)

Accuracy was improved for comparisons between DECIMAL columns and numbers represented as strings. (Bug#23260)

Calculation of COUNT(DISTINCT), AVG(DISTINCT), or SUM(DISTINCT) when they are referenced more than once in a single query with GROUP BY could cause a server crash. (Bug#23184)

InnoDB crashed while performing XA recovery of prepared transactions. (Bug#21468)

Certain malformed INSERT statements could crash the mysql client. (Bug#21142)

CONCURRENT did not work correctly for LOAD DATA INFILE. (Bug#20637)

Several string functions could return incorrect results when given very large length arguments. (Bug#10963)