Important Change: Incompatible Change: The FEDERATED storage engine is now disabled by default in binary distributions. The engine is still available and can be enabled by starting the server with the --federated option. (Bug #37069)

mysqltest was changed to be more robust in the case of a race condition that can occur for rapid disconnect/connect sequences with the server. The account used by mysqltest could reach its permitted simultaneous-sessions user limit if the connect attempt occurred before the server had fully processed the preceding disconnect. mysqltest now checks specificaly for a user-limits error when it connects; if that error occurs, it delays briefly before retrying. (Bug #23921)

Replication: Row-based replication broke for utf8 CHAR columns longer than 85 characters. (Bug #37426)

Replication: Performing an insert on a table having an AUTO_INCREMENT column and an INSERT trigger that was being replicated from a master running MySQL 5.0 or any version of MySQL 5.1 up to and including MySQL 5.1.11 to a slave running MySQL 5.1.12 or later caused the replication slave to crash. (Bug #36443)

References: See also Bug #33029.

Some binary distributions had a duplicate “-64bit” suffix in the file name. (Bug #37623)

NOT IN subqueries that selected MIN() or MAX() values but produced an empty result could cause a server crash. (Bug #37004)

ha_innodb.so was incorrectly installed in the lib/mysql directory rather than in lib/mysql/plugin. (Bug #36434)

An empty bit-string literal (b'') caused a server crash. Now the value is parsed as an empty bit value (which is treated as an empty string in string context or 0 in numeric context). (Bug #35658)

The code for detecting a byte order mark (BOM) caused mysql to crash for empty input. (Bug #35480)

The mysql client incorrectly parsed statements containing the word “delimiter” in mid-statement.

The fix for this bug had the side effect of causing the problem reported in Bug #38158, so it was reverted in MySQL 5.1.27. (Bug #33812)