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)

Incompatible Change: The engines column in the mysql.online_backup table has been renamed to drivers to better reflect its contents. (Bug#34965)

Incompatible Change: A change has been made to the way that the server handles prepared statements. This affects prepared statements processed at the SQL level (using the PREPARE statement) and those processed using the binary client-server protocol (using the mysql_stmt_prepare() C API function).

Previously, changes to metadata of tables or views referred to in a prepared statement could cause a server crash when the statement was next executed, or perhaps an error at execute time with a crash occurring later. For example, this could happen after dropping a table and recreating it with a different definition.

Now metadata changes to tables or views referred to by prepared statements are detected and cause automatic repreparation of the statement when it is next executed. Metadata changes occur for DDL statements such as those that create, drop, alter, rename, or truncate tables, or that analyze, optimize, or repair tables. Repreparation also occurs after referenced tables or views are flushed from the table definition cache, either implicitly to make room for new entries in the cache, or explicitly due to FLUSH TABLES.

Repreparation is automatic, but to the extent that it occurs, performance of prepared statements is diminished.

Table content changes (for example, with INSERT or UPDATE) do not cause repreparation, nor do SELECT statements.

An incompatibility with previous versions of MySQL is that a prepared statement may now return a different set of columns or different column types from one execution to the next. For example, if the prepared statement is SELECT * FROM t1, altering t1 to contain a different number of columns causes the next execution to return a number of columns different from the previous execution.

Older versions of the client library cannot handle this change in behavior. For applications that use prepared statements with the new server, an upgrade to the new client library is strongly recommended.

Along with this change to statement repreparation, the default value of the table_definition_cache system variable has been increased from 128 to 256. The purpose of this increase is to lessen the chance that prepared statements will need repreparation due to referred-to tables/views having been flushed from the cache to make room for new entries.

A new status variable, Com_stmt_reprepare, has been introduced to track the number of repreparations. (Bug#27420, Bug#27430, Bug#27690)

Important Change: Some changes were made to CHECK TABLE ... FOR UPGRADE and REPAIR TABLE with respect to detection and handling of tables with incompatible .frm files (files created with a different version of the MySQL server). These changes also affect mysqlcheck because that program uses CHECK TABLE and REPAIR table, and thus also mysql_upgrade because that program invokes mysqlcheck.

(Bug#36055)

Important Change: The Maria Storage Engine is now available as standard. Maria is a crash safe version of MyISAM. Maria supports all of the main functionality of the MyISAM engine, but includes recovery support (in the event of a system crash), full logging (including CREATE, DROP, RENAME, and TRUNCATE operations), all MyISAM row formats and a new Maria-specific row format. Maria is documented at Section 13.5, “The Maria Storage Engine”.

Important Note: When MySQL is built with the Maria engine, all internal temporary on disk tables will use the Maria engine. Using Maria temporary tables in plkace of MyISAM tables should result in a performance gain.

On Unix, it is now possible for the output file for BACKUP DATABASE to be an existing FIFO. (Bug#37012)

mysql_upgrade now has a --tmpdir option to enable the location of temporary files to be specified. (Bug#36469)

mysqldump now adds the LOCAL qualifier to the FLUSH TABLES statement that is sent to the server when the --master-data option is enabled. This prevents the FLUSH TABLES statement from replicating to slaves, which is disadvantageous because it would cause slaves to block while the statement executes. (Bug#35157)

See also Bug#38303

The use of the SQL_CACHE and SQL_NO_CACHE options in SELECT statements now is checked more restrictively: 1) Previously, both options could be given in the same statement. This is no longer true; only one can be given. 2) Previously, these options could be given in SELECT statements that were not at the top-level. This is no longer true; the options are disallowed in subqueries (including subqueries in the FROM clause, and SELECT statements in unions other than the first SELECT. (Bug#35020)

The undocumented, deprecated, and not useful SHOW COLUMN TYPES statement has been removed. (Bug#5299)

The server now supports a Debug Sync facility for thread synchronization during testing and debugging. To compile in this facility, configure MySQL with the --enable-debug-sync option. The debug_sync system variable provides the user interface Debug Sync. mysqld and mysql-test-run.pl support a --debug-sync-timeout option to enable the facility and set the default synchronization point timeout.

mysql-test-run.pl now supports a --mysqltest option for specifying options to the mysqltest program.

Several improvements were made to MySQL Backup (the BACKUP DATABASE and RESTORE statements):

BACKUP DATABASE now has a WITH COMPRESSION clause. This causes the image file to be compressed, which reduces its size. Compression also may result in improved backup time by reducing writes to disk.

Incompatible Change: Access privileges for several statements are more accurately checked:

(Bug#27145)

Incompatible Change: Certain characters were sorted incorrectly for the following collations: TILDE and GRAVE ACCENT in big5_chinese_ci; LATIN SMALL LETTER J in cp866_general_ci; TILDE in gb2312_chinese_ci; and TILDE in gbk_chinese_ci.

As a result of this fix, any indexes on columns that use these collations and contain the affected characters must be rebuilt when upgrading to 6.0.6 or higher. To do this, use ALTER TABLE to drop and re-add the indexes, or mysqldump to dump the affected tables and mysql to reload the dump file. (Bug#25420)

Incompatible Change: An additional correction to the original MySQL 6.0.4 fix was made to normalize directory names before adding them to the list of directories. This prevents /etc/ and /etc from being considered different, for example. (Bug#20748)

See also Bug#38180

Important Change: The server no longer issues warnings for truncation of excess spaces for values inserted into CHAR columns. This reverts a change in the previous release that caused warnings to be issued. (Bug#30059)

Partitioning: When one user was in the midst of a transaction on a partitioned table, a second user performing an ALTER TABLE on this table caused the server to hang. (Bug#34604)

Partitioning: Inserts failed on partitioned tables containing user-supplied values for an AUTO_INCREMENT column. (Bug#33479)

Replication: CREATE PROCEDURE and CREATE FUNCTION statements containing extended comments were not written to the binary log correctly, causing parse errors on the slave. (Bug#36570)

See also Bug#32575

Replication: When flushing tables, there was a slight chance that the flush occurred between the processing of one table map event and the next. Since the tables were opened one by one, subsequent locking of tables would cause the slave to crash. This problem was observed when replicating NDBCLUSTER or InnoDB tables, when executing multi-table updates, and when a trigger or a stored routine performed an (additional) insert on a table so that two tables were effectively being inserted into in the same statement. (Bug#36197)

Replication: CREATE VIEW statements containing extended comments were not written to the binary log correctly, causing parse errors on the slave. Now, all comments are stripped from such statements before being written to the binary log. (Bug#32575)

See also Bug#36570

The Windows my-template.ini template file contained a reference to the myisam_max_extra_sort_file_size system variable, which no longer exists, causing the installed server to fail upon startup. (Bug#38371)

The fix for Bug#33812 had the side effect of causing the mysql client not to be able to read some dump files produced with mysqldump. To address this, that fix was reverted. (Bug#38158)

The MyISAM backup driver was subject to a race condition that allowed multiple RESTORE operations to occur simultaneously. This could result in locking conflicts, incorrect entries in the progress tables, or other problems. (Bug#38108)

Building MySQL with SSL and Falcon enabled would lead to a build failure. (Bug#37517)

The code for the ut_usectime() function in InnoDB did not handle errors from the gettimeofday() system call. Now it retries gettimeofday() several times and updates the value of the Innodb_row_lock_time_max status variable only if ut_usectime() was successful. (Bug#36819)

If the length of a field was 3, internal InnoDB to integer type conversion didn't work on big-endian machines in the row_search_autoinc_column() function. (Bug#36793)

For a view that referred to a MyISAM table, the contents of the table could be empty after BACKUP DATABASE followed by RESTORE. (Bug#36782)

Data loss could be caused by attempts to read data from a database being restored by a RESTORE operation. (Bug#36778)

Data loss could be caused by activation of a trigger for a MyISAM table being restored by a RESTORE operation. (Bug#36749)

On Windows 64-bit systems, temporary variables of long types were used to store ulong values, causing key cache initialization to receive distorted parameters. The effect was that setting key_buffer_size to values of 2GB or more caused memory exhaustion to due allocation of too much memory. (Bug#36705)

Multiple-table UPDATE statements that used a temporary table could fail to update all qualifying rows or fail with a spurious duplicate-key error. (Bug#36676)

The online backup stream library failed to parse the backup stream on 64-bit systems. (Bug#36624)

SHOW STATUS took a lot of CPU time for calculating the value of the Innodb_buffer_pool_pages_latched status variable. Now this variable is calculated and included in the output of SHOW STATUS only when the UNIV_DEBUG symbol is defined at server build time. (Bug#36600)

On 64-bit platforms, BACKUP DATABASE hung for backups of more than 32KB. (Bug#36586)

Dumping information about locks in use by sending a SIGHUP signal to the server or by invoking the mysqladmin debug command could lead to a server crash in debug builds or to undefined behavior in production builds. (Bug#36579)

A REGEXP match could return incorrect rows when the previous row matched the expression and used CONCAT() with an empty string. (Bug#36488)

mysqltest ignored the value of --tmpdir in one place. (Bug#36465)

The ER_TRUNCATED_WRONG_VALUE warning condition was sometimes raised as an error. (Bug#36457)

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

The default drivers for BACKUP DATABASE and RESTORE now support a cancel operation, which also allows better cleanup if a driver error occurs. (Bug#36323)

The server crashed while parsing large floating-point numbers such as 1e37 or -1e15. (Bug#36320)

When updating an existing instance (for example, from MySQL 5.0 to 5.1, or 5.1 to 6.0), the Instance Configuration Wizard unnecessarily prompted for a root password when there was an existing root password. (Bug#36305)

For InnoDB tables, the DATA_FREE column of the INFORMATION_SCHEMA.TABLES displayed free space in kilobytes rather than bytes. Now it displays bytes. (Bug#36278)

BACKUP DATABASE failed to back up views that depend on tables in a different database. (Bug#36265)

The project files created for Windows were missing the GenError project dependency. (Bug#36257)

The mysql client failed to recognize comment lines consisting of -- followed by a newline. (Bug#36244)

CREATE INDEX for InnoDB tables could under very rare circumstances cause the server to crash.. (Bug#36169)

A read past the end of the string could occur while parsing the value of the --innodb-data-file-path option. (Bug#36149)

Conversion of a FLOAT ZEROFILL value to string could cause a server crash if the value was NULL. (Bug#36139)

The combination of semi-join and materialization both being enabled could lead to assertion failure during subquery processing. (Bug#36137)

Range optimizer evaluation of IN subqueries to be handled with the materialization strategy could lead to assertion failure. (Bug#36133)

A server crash could occur during the cleanup phase of subquery execution. (Bug#36128)

On Windows, the installer attempted to use JScript to determine whether the target data directory already existed. On Windows Vista x64, this resulted in an error because the installer was attempting to run the JScript in a 32-bit engine, which wasn't registered on Vista. The installer no longer uses JScript but instead relies on a native WiX command. (Bug#36103)

mysqltest was performing escape processing for the --replace_result command, which it should not have been. (Bug#36041)

An error in calculation of the precision of zero-length items (such as NULL) caused a server crash for queries that employed temporary tables. (Bug#36023)

For EXPLAIN EXTENDED, execution of an uncorrelated IN subquery caused a crash if the subquery required a temporary table for its execution. (Bug#36011)

The MERGE storage engine did a table scan for SELECT COUNT(*) statements when it could calculate the number of records from the underlying tables. (Bug#36006)

The server crashed inside NOT IN subqueries with an impossible WHERE or HAVING clause, such as NOT IN (SELECT ... FROM t1, t2, ... WHERE 0). (Bug#36005)

mysql_stmt_prepare() did not reset the list of messages (those messages available via SHOW WARNINGS). (Bug#36004)

The Event Scheduler was not designed to work under the embedded server. It is now disabled for the embedded server, and the event_scheduler system variable is not displayed. (Bug#35997)

Grouping or ordering of long values in unindexed BLOB or TEXT columns with the gbk or big5 character set crashed the server. (Bug#35993)

SET GLOBAL debug='' resulted in a Valgrind warning in DbugParse(), which was reading beyond the end of the control string. (Bug#35986)

If a SELECT table list contained at least one INFORMATION_SCHEMA table, the required privileges for accessing the other tables were reduced. (Bug#35955)

Some syntactically invalid statements could cause the server to return an error message containing garbage characters. (Bug#35936)

The “prefer full scan on clustered primary key over full scan of any secondary key” optimizer rule introduced by Bug#26447 caused a performance regression for some queries, so it has been disabled. (Bug#35850)

The server ignored any covering index used for ref access of a table in a query with ORDER BY if this index was incompatible with the ORDER BY list and there was another covering index compatible with this list. As a result, suboptimal execution plans were chosen for some queries that used an ORDER BY clause. (Bug#35844)

mysql_upgrade did not properly update the mysql.event table. (Bug#35824)

The current system time (as returned by NOW() or synonyms) became constant after a RESTORE operation. (Bug#35806)

Processing of an uncorrelated subquery using semi-join could cause incorrect results or a server crash. (Bug#35767)

An incorrect error and message was produced for attempts to create a MyISAM table with an index (.MYI) filename that was already in use by some other MyISAM table that was open at the same time. For example, this might happen if you use the same value of the INDEX DIRECTORY table option for tables belonging to different databases. (Bug#35733)

Enabling the read_only system variable while autocommit mode was enabled caused SELECT statements for transactional storage engines to fail. (Bug#35732)

The range optimizer ignored conditions on inner tables in semi-join IN subqueries, causing the the optimizer to miss good query execution plans. (Bug#35674)

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)

For InnoDB tables, REPLACE statements used “traditional” style locking, regardless of the setting of innodb_autoinc_lock_mode. Now REPLACE works the same way as “simple inserts” instead of using the old locking algorithm. (REPLACE statements are treated in the same way as as INSERT statements.) (Bug#35602)

Different invocations of CHECKSUM TABLE could return different results for a table containing columns with spatial data types. (Bug#35570)

A semi-join subquery in the ON clause in the absence of a WHERE clause caused a server crash. (Bug#35550)

InnoDB was not updating the Handler_delete or Handler_update status variables. (Bug#35537)

If the server crashed with an InnoDB error due to unavailability of undo slots, errors could persist during rollback when the server was restarted: There are two UNDO slot caches (for INSERT and UPDATE). If all slots end up in one of the slot caches, a request for a slot from the other slot cache would fail. This can happen if the request is for an UPDATE slot and all slots are in the INSERT slot cache, or vice versa. (Bug#35352)

The combination of GROUP_CONCAT(), DISTINCT, and LEFT JOIN could crash the server when the right table is empty. (Bug#35298)

Accessing a MERGE table with an empty underlying table list incorrectly resulted in a “wrong index” error message rather than “end of file.” (Bug#35274)

BACKUP DATABASE caused a server crash upon encountering a table row that has been marked for deletion but not removed. (Bug#35249)

For InnoDB tables, ALTER TABLE DROP failed if the name of the column to be dropped began with “foreign”. (Bug#35220)

The table pullout strategy was not reflected in EXPLAIN EXTENDED output if not all of the subquery tables were pulled out. (Bug#35160)

Access-denied messages for INFORMATION_SCHEMA incorrectly showed the name of the default database instead. (Bug#35096)

Passing an invalid parameter to CHAR() in an ORDER BY clause caused the server to hang. (Bug#34949)

Some binaries produced stack corruption messages due to being built with versions of bison older than 2.1. Builds are now created using bison 2.3. (Bug#34926)

Concurrent execution of FLUSH TABLES along with SHOW FUNCTION STATUS or SHOW PROCEDURE STATUS could cause a server crash. (Bug#34895)

The log_output system variable could be set to an illegal value. (Bug#34820)

A server crash or memory overrun could occur with a dependent subquery and joins. (Bug#34799)

InnoDB could crash if overflow occurred for an AUTO_INCREMENT column. (Bug#34335)

On Windows 64-bit builds, an apparent compiler bug caused memory overruns for code in innobase/mem/*. Removed optimizations so as not to trigger this problem. (Bug#34297)

Several additional configuration scripts in the BUILD directory now are included in source distributions. These may be useful for users who wish to build MySQL from source. (See Section 2.9.3, “Installing from the Development Source Tree”, for information about what they do.) (Bug#34291)

For InnoDB tables, loss of data resulted from performing inserts concurrently with a RESTORE operation. (Bug#34210)

A number of problems in new subquery optimization code meant that MySQL could pick an incorrect query plan when using InsideOut and/or FirstMatch subquery optimizations, which in turn would cause wrong query results. (Bug#33743)

TIMESTAMP columns were restored to the current date and time (not their actual values) by a RESTORE operation. (Bug#33573)

Use of 61 nested subqueries caused a server crash. (Bug#33509)

For InnoDB tables, there was a race condition involving the data dictionary and repartitioning. (Bug#33349)

Executing a FLUSH PRIVILEGES statement after creating a temporary table in the mysql database with the same name as one of the MySQL system tables caused the server to crash.

(Bug#33275)

Selecting from a view that referenced the same table in the FROM clause and an IN clause caused a server crash. (Bug#33245)

There was a race condition between the event scheduler and the server shutdown thread. (Bug#32771)

Assignment of relative pathnames to general_log_file or slow_query_log_file did not always work. (Bug#32748)

Deeply nested subqueries could cause stack overflow or a server crash. (Bug#32680)

Conversion of binary values to multi-byte character sets could fail to left-pad values to the correct length. This could result in a server crash. (Bug#32394)

Killing a statement that invoked a stored function could return an incorrect error message indicating table corruption rather than that the statement had been interrupted. (Bug#32140)

Occurrence of an error within a stored routine did not always cause immediate statement termination. (Bug#31881)

For DROP FUNCTION db_name.func_name (that is, when the function name is qualified with the database name), the statement should apply only to a stored function named func_name in the given database. However, if a UDF with the same name existed, the statement dropped the UDF instead. (Bug#31767)

TRUNCATE TABLE for InnoDB tables returned a count showing too many rows affected. Now the statement returns 0 for InnoDB tables. (Bug#29507)

InnoDB could return an incorrect rows-updated value for UPDATE statements. (Bug#29157)

The mysql.servers table was not created during installation on Windows. (Bug#28680, Bug#32797)

The jp test suite was not working. (Bug#28563)

The internal init_time() library function was renamed to my_init_time() to avoid conflicts with external libraries. (Bug#26294)

In some cases, the parser interpreted the ; character as the end of input and misinterpreted stored program definitions. (Bug#26030)

Statements to create, alter, or drop a view were not waiting for completion of statements that were using the view, which led to incorrect sequences of statements in the binary log when statement-based logging was enabled. (Bug#25144)

The Questions status variable is intended as a count of statements sent by clients to the server, but was also counting statements executed within stored routines. (Bug#24289)

InnoDB exhibited thread thrashing with more than 50 concurrent connections under an update-intensive workload. (Bug#22868)

DROP DATABASE did not drop orphaned FOREIGN KEY constraints. (Bug#18942)

Delayed-insert threads were counted as connected but not as created, incorrectly leading to a Threads_connected value greater than the Threads_created value. (Bug#17954)

The parser used signed rather than unsigned values in some cases that caused legal lengths in column declarations to be rejected. (Bug#15776)

Stored procedure exception handlers were catching fatal errors (such as out of memory errors), which could cause execution not to stop to due a continue handler. Now fatal errors are not caught by exception handlers and a fatal error is returned to the client. (Bug#15192)

On Windows, moving an InnoDB .ibd file and then symlinking to it in the database directory using a .sym file caused a server crash. (Bug#11894)

If a connection was waiting for a GET_LOCK() lock or a SLEEP() call, and the connection aborted, the server did not detect this and thus did not close the connection. This caused a waste of system resources allocated to dead connections. Now the server checks such a connection every five seconds to see whether it has been aborted. If so, the connection is killed (and any lock request is aborted). (Bug#10374)