Incompatible Change: The tables for MySQL Backup logging have been renamed, and the logging capabilities now are more flexible, similar to the capabilities provided for the general query log and slow query log.

Important Change: The --skip-thread-priority option is now deprecated in MySQL 5.1 and is removed in MySQL 6.0 such that the server won't change the thread priorities by default. Giving threads different priorities might yield marginal improvements in some platforms (where it actually works), but it might instead cause significant degradation depending on the thread count and number of processors. Meddling with the thread priorities is a not a safe bet as it is very dependent on the behavior of the CPU scheduler and system where MySQL is being run. (Bug#35164, Bug#37536)

Important Change: The --log option now is deprecated and will be removed (along with the log system variable) in the future. Instead, use the --general_log option to enable the general query log and the --general_log_file=file_name option to set the general query log filename. The values of these options are available in the general_log and general_log_file system variables, which can be changed at runtime.

Similar changes were made for the --log-slow-queries option and log_slow_queries system variable. You should use the --slow_query_log and --slow_query_log_file=file_name options instead (and the slow_query_log and slow_query_log_file system variables).

The BUILD/compile-solaris-* scripts now compile MySQL with the mtmalloc library rather than malloc. (Bug#38727)

Binary distributions for Solaris, Linux, and Mac OS X now are built with support for the pool-of-threads value of thread_handling. (Bug#38636)

BACKUP DATABASE now performs an implicit commit, like RESTORE. (Bug#38261)

The deprecated --default-table-type server option has been removed. (Bug#34818)

On WIndows, use of POSIX I/O interfaces in mysys was replaced with Win32 API calls (CreateFile(), WriteFile(), and so forth) and the default maximum number of open files has been increased to 16384. The maximum can be increased further by using the --max-open-files=N option at server startup. (Bug#24509)

MySQL now supports an interface for semisynchronous replication: A commit performed on the master side blocks before returning to the session that performed the transaction until at least one slave acknowleges that it has received and logged the events for the transaction. Semisynchronous replication is implemented through an optional plugin component. See Section 16.2.9, “Semisynchronous Replication”

Most statements that previously caused an implicit commit before executing now also cause an implicit commit after executing. Also, the FLUSH statement and mysql_refresh() C API function now cause an implicit commit. See Section 12.4.3, “Statements That Cause an Implicit Commit”.

Incompatible Change: CHECK TABLE ... FOR UPGRADE did not check for incompatible collation changes made in MySQL 5.0.48. (This also affects mysqlcheck and mysql_upgrade, which cause that statement to be executed.) (Bug#39585)

See also Bug#40984.

Incompatible Change: In connection with view creation, the server created arc directories inside database directories and maintained useless copies of .frm files there. Creation and renaming procedures of those copies as well as creation of arc directories has been discontinued.

This change does cause a problem when downgrading to older server versions which manifests itself under these circumstances:

As a workaround to avoid this problem, use either of these approaches:

The downgrade problem introduced by the fix for this bug has been addressed as Bug#40021. (Bug#17823)

Important Change: Replication: The SUPER privilege is now required to change the session value of binlog_format as well as its global value. For more information about binlog_format, see Section 16.1.2, “Replication Formats”. (Bug#39106)

Partitioning: Replication: Replication to partitioned MyISAM tables could be slow with row-based binary logging. (Bug#35843)

Partitioning: A duplicate key error raised when inserting into a partitioned table used a different error code from that returned by such an error raised when inserting into a table that was not partitioned. (Bug#38719)

See also Bug#28842.

Partitioning: If an error occurred when evaluating a column of a partitioned table for the partitioning function, the row could be inserted anyway. (Bug#38083)

Partitioning: Using INSERT ... SELECT to insert records into a partitioned MyISAM table could fail if some partitions were empty and others are not. (Bug#38005)

Replication: Replication of BLACKHOLE tables did not work with row-based binary logging. (Bug#38360)

Replication: In some cases, a replication master sent a special event to a reconnecting slave to keep the slave's temporary tables, but they still had references to the “old” slave SQL thread and used them to access that thread's data. (Bug#38269)

Replication: Replication filtering rules were inappropiately applied when executing BINLOG pseudo-queries. One way in which this problem showed itself was that, when replaying a binary log with mysqlbinlog, RBR events were sometimes not executed if the --replicate-do-db option was specified. Now replication rules are applied only to those events executed by the slave SQL thread. (Bug#36099)

Replication: For a CREATE TABLE ... SELECT statement that creates a table in a database other than the current one, the table could be created in the wrong database on replication slaves if row-based binary logging is used. (Bug#34707)

Replication: A statement did not always commit or roll back correctly when the server was shut down; the error could be triggered by having a failing UPDATE or INSERT statement on a transactional table, causing an implicit rollback. (Bug#32709)

See also Bug#38262.

Compiling using --with-falcon on Mac OS X fails if you use CXX=gcc. You must specify that the g++ compiler should be used for C++ using CXX=g++. (Bug#41270)

Creating a table, or selecting from a table using the FALCON storage engine and with a double quote in the name would cause an assertion failure. (Bug#40158, Bug#39388)

Windows builds were missing the MySQL Backup log tables. (Bug#40126)

The indexes and record contents of a FALCON table could get out of synchronization during a lrge number of updates. Because FALCON returns data only if it matches both the index and record data the result sets returned could be invalid when comparing the results of an index and non-index based SELECT. (Bug#40112, Bug#40130)

The CHECK TABLE ... FOR UPGRADE statement did not check for incompatible collation changes made in MySQL 5.1.24. (This also affects mysqlcheck and mysql_upgrade, which cause that statement to be executed.)

Prior to this fix, a binary upgrade (performed without dumping tables with mysqldump before the upgrade and reloading the dump file after the upgrade) would corrupt tables. After the fix, CHECK TABLE ... FOR UPGRADE properly detects the problem and upgrades tables.

However, the fix is not backward compatible and can result in a downgrading problem under these circumstances:

The solution is to dump tables with mysqldump before the downgrade and reload the dump file after the downgrade. Alternatively, drop and recreate affected indexes. (Bug#40053)

Non-ASCII error messages were corrupted. (Bug#39949)

The Threads_created status variable was not correctly incremented when the server was started with the --thread-handling=pool-of-threads option. (Bug#39916)

On Windows Vista, RESTORE did not correctly calculate the validity point from the backup stream. (Bug#39825)

When creating a table with the FALCON engine where the size of the key in the index was larger than supported (the error message did not signify the severity of the problem. The message and error has been updated. (Bug#39708)

The MySQL Backup backup_history log now contains a backup_file_path column. backup_file contains the basename and backup_file_path contains the directory of the image file pathname. (Bug#39690)

Some MySQL Backup-related memory-use warnings detected by Valgrind were corrected. (Bug#39598)

Creating a table with a comment of 62 characters or longer caused a server crash. (Bug#39591)

The Sun Studio compiler failed to build debug versions of the server due to use of features specific to gcc. (Bug#39451)

For a TIMESTAMP column in an InnoDB table, testing the column with multiple conditions in the WHERE clause caused a server crash. (Bug#39353)

For BACKUP DATABASE, the server could add a / character to the end of the backup path, even when the path ended with a filename rather than a directory name. (Bug#39189)

The server could crash when attempting to insert duplicate empty strings into a utf8 SET column. (Bug#39186)

References to local variables in stored procedures are replaced with NAME_CONST(name, value) when written to the binary log. However, an “illegal mix of collation” error might occur when executing the log contents if the value's collation differed from that of the variable. Now information about the variable collation is written as well. (Bug#39182)

BACKUP DATABASE failed on PowerMac platforms due to type casting problems. (Bug#39127)

MySQL Backup was not handling several errors. (Bug#39089)

Some warnings were being reported as errors. (Bug#39059)

Queries of the form SELECT ... REGEXP BINARY NULL could lead to a hung or crashed server. (Bug#39021)

Statements of the form INSERT ... SELECT .. ON DUPLICATE KEY UPDATE col_name = DEFAULT could result in a server crash. (Bug#39002)

Repeated CREATE TABLE ... SELECT statements, where the created table contained an AUTO_INCREMENT column, could lead to an assertion failure. (Bug#38821)

RESTORE crashed if a trigger and an event had the same name. (Bug#38810)

For deadlock between two transactions that required a timeout to resolve, all server tables became inaccessible for the duration of the deadlock. (Bug#38804)

When inserting a string into a duplicate-key error message, the server could improperly interpret the string, resulting in a crash. (Bug#38701)

A race condition between threads sometimes caused unallocated memory to be addressed. (Bug#38692)

A server crash resulted from concurrent execution of a multiple-table UPDATE that used a NATURAL or USING join together with FLUSH TABLES WITH READ LOCK or ALTER TABLE for the table being updated. (Bug#38691)

On ActiveState Perl, mysql-test-run.pl --start-and-exit started but did not exit. (Bug#38629)

A server crash resulted from execution of an UPDATE that used a derived table together with FLUSH TABLES. (Bug#38499)

Stored procedures involving substrings could crash the server on certain platforms due to invalid memory reads. (Bug#38469)

The binary log filename stored in the binlog_file column of the mysql.backup_history MySQL Backup table now is the file basename (the final component). Previously, the full pathname was stored, but this could be too long for the column width. (Bug#38462)

On Windows, starting the server with the --external-locking=1 option caused BACKUP DATABASE to fail. (Bug#38342)

Errors during server startup caused destruction of an uninitialized mutex and assertion failure. (Bug#37961)

The handlerton-to-plugin mapping implementation did not free handler plugin references when the plugin was uninstalled, resulting in a server crash after several install/uninstall cycles. Also, on Mac OS X, the server crashed when trying to access an EXAMPLE table after the EXAMPLE plugin was installed. (Bug#37958)

The server crashed if an argument to a stored procedure was a subquery that returned more than one row. (Bug#37949)

When analyzing the possible index use cases, the server was incorrectly reusing an internal structure, leading to a server crash. (Bug#37943)

Access checks were skipped for SHOW PROCEDURE STATUS and SHOW FUNCTION STATUS, which could lead to a server crash or insufficient access checks in subsequent statements. (Bug#37908)

Comparisons could hang for SET or ENUM columns that used latin2_czech_cs collation. (Bug#37854)

SHOW PROCESSLIST displayed “copy to tmp table” when no such copy was occurring. (Bug#37550)

The <=> operator could return incorrect results when comparing NULL to DATE, TIME, or DATETIME values. (Bug#37526)

MySQL Backup was not consistently checking for BSTREAM_ERROR errors. (Bug#37522)

The combination of a subquery with a GROUP BY, an aggregate function calculated outside the subquery, and a GROUP BY on the outer SELECT could cause the server to crash. (Bug#37348)

Incorrect BLOB handling by RESTORE could result in a server crash. (Bug#37212)

The NO_BACKSLASH_ESCAPES SQL mode was ignored for LOAD DATA INFILE and SELECT INTO ... OUTFILE. The setting is taken into account now. (Bug#37114)

If thread-pooling was used and a connection attempt was denied on the grounds of exceeding the user limits, the number of active connections for that user was erroneously decreased twice. The difference between the actual number connections and the internal count could then cause debug builds of the server to raise an assertion. (Bug#36970)

Long error messages for RESTORE could be truncated. (Bug#36854)

In some cases, references to views were confused with references to anonymous tables and privilege checking was not performed. (Bug#36086)

For crash reports on Windows, symbol names in stack traces were not correctly resolved. (Bug#35987)

ALTER EVENT changed the PRESERVE attribute of an event even when PRESERVE was not specified in the statement. (Bug#35981)

Hostname values in SQL statements were not being checked for '@', which is illegal according to RFC952. (Bug#35924)

mysql_install_db failed on machines that had the hostname set to localhost. (Bug#35754)

Dynamic plugins failed to load on i5/OS. (Bug#35743)

With the PAD_CHAR_TO_FULL_LENGTH SQL mode enabled, a ucs2 CHAR column returned additional garbage after trailing space characters. (Bug#35720)

RESTORE did not set the validity_point_time, binlog_pos, and binlog_file fields of the backup_history log table row. (Bug#35240)

With binary logging enabled, CREATE TABLE ... SELECT failed if the source table was a log table. (Bug#34306)

If BACKUP DATABASE and RESTORE were done in a session with autocommit disabled, a later DROP TABLE or RESTORE in the same session failed. (Bug#34204)

The secure_file_priv system variable now applies to BACKUP DATABASE and RESTORE operations: If the value is nonempty, backup and restore operations can read and write files only in the given directory. (Bug#34171)

mysql_real_connect() did not check whether the MYSQL connection handler was already connected and connected again even if so. Now an CR_ALREADY_CONNECTED error occurs. (Bug#33831)

Shutting down the MySQL Server immediately following the execution of a BACKUP DATABASE statement caused the server to crash if the database to be backed up contained any Falcon tables. (Bug#33575)

The server crashed for BACKUP DATABASE if the backup progress tables in the mysql database were missing or created incorrectly. (Bug#33352)

CHECKSUM TABLE was not killable with KILL QUERY. (Bug#33146)

A trigger for an InnoDB table activating multiple times could lead to AUTO_INCREMENT gaps. (Bug#31612)

mysqldump could fail to dump views containing a large number of columns. (Bug#31434)

The server could improperly type user-defined variables used in the select list of a query. (Bug#26020)

For access to the INFORMATION_SCHEMA.VIEWS table, the server did not check the SHOW VIEW and SELECT provileges, leading to inconsistency between output from that table and the SHOW CREATE VIEW statement. (Bug#22763)

mysqld_safe would sometimes fail to remove the pid file for the old mysql process after a crash. As a result, the server would fail to start due to a false A mysqld process already exists... error. (Bug#11122)