MySQL :: MySQL 5.6 Release Notes :: Changes in MySQL 5.6.5 (2012-04-10, Milestone 8)

MySQL 5.6 Release Notes / Changes in MySQL 5.6.5 (2012-04-10, Milestone 8)

Changes in MySQL 5.6.5 (2012-04-10, Milestone 8)

Note

This is a milestone release, for use at your own risk. Upgrades between milestone releases (or from a milestone release to a GA release) are not supported. Significant development changes take place in milestone releases and you may encounter compatibility issues, such as data format changes that require attention in addition to the usual procedure of running mysql_upgrade. For example, you may find it necessary to dump your data with mysqldump before the upgrade and reload it afterward. (Making a backup before the upgrade is a prudent precaution in any case.)

Beginning with MySQL 5.6.5, Oracle no longer provides binaries for OS X 10.5. This aligns with Apple no longer providing updates or support for this platform.

Data Type Notes

Previously, at most one TIMESTAMP column per table could be automatically initialized or updated to the current date and time. This restriction has been lifted. Any TIMESTAMP column definition can have any combination of DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses. In addition, these clauses now can be used with DATETIME column definitions. For more information, see Automatic Initialization and Updating for TIMESTAMP and DATETIME.

Replication with GTIDs

Important Change; Replication: This release introduces global transaction identifiers (GTIDs) for MySQL Replication. A GTID is a unique identifier that is assigned to each transaction as it is committed; this identifier is unique on the MySQL Server where the transaction originated, as well as across all MySQL Servers in a given replication setup. Because GTID-based replication depends on tracking transactions, it cannot be employed with tables that employ a nontransactional storage engine such as MyISAM; thus, it is currently supported only with InnoDB tables.

Because each transaction is uniquely identified, it is not necessary when using GTIDs to specify positions in the master's binary log when starting a new slave or failing over to a new master. This is reflected in the addition of a new MASTER_AUTO_POSITION option for the CHANGE MASTER TO statement which takes the place of the MASTER_LOG_FILE and MASTER_LOG_POS options when executing this statement to prepare a MySQL Server to act as a replication slave.

To enable GTIDs on a MySQL Server, the server must be started with the options --gtid-mode=ON --disable-gtid-unsafe-statements --log-bin --log-slave-updates. These options are needed whether the server acts as a replication master or as a replication slave; the --gtid-mode and --disable-gtid-unsafe-statements options are new in this release. Once the master and slave have each been started with these options, it is necessary only to issue a CHANGE MASTER TO ... MASTER_AUTO_POSITION=1 followed by START SLAVE on the slave to start replication.

A number of new server system variables have also been added for monitoring GTID usage. For more information about these options and variables, see Global Transaction ID Options and Variables.

As part of these changes, three new mysqlbinlog options—--include-gtids, --exclude-gtids, and --skip-gtids—have been added for reading binary logs produced when the server participates in replication with GTIDs.

Important

Due to an issue discovered just prior to release, you cannot import a dump made using mysqldump from a MySQL 5.5 server to a MySQL 5.6.5 server and then use mysqlupgrade on the MySQL 5.6.5 server while GTIDs are enabled; doing so makes it impossible to connect to the server normally following the upgrade. Instead, you should import the dump and run mysqlupgrade while the MySQL 5.6.5 server is running with --gtid-mode=OFF, then restart it with --gtid-mode=ON. (Bug #13833710) (mysqlupgrade can be executed when the server is running with --gtid-mode set either to OFF, or to ON.)

For additional information about GTIDs and setting up GTID-based replication, see Replication with Global Transaction Identifiers.

Host Cache Notes

MySQL now provides improved access to the host cache, which contains client IP address and host name information and is used to avoid DNS lookups, as well as more information about the causes of errors that occur when clients connect to the server. These changes have been implemented:
- A new Performance Schema host_cache table exposes the contents of the host cache so that it can be examined using SELECT statements. Access to host cache contents makes it possible to answer questions such as how many hosts are cached, what kinds of connection errors are occurring for which hosts, or how close host error counts are to reaching the max_connect_errors system variable limit. The Performance Schema must be enabled or this table is empty.
  
  If you upgrade to this MySQL release from an earlier version, you must run mysql_upgrade (and restart the server) to incorporate this change into the performance_schema database.
- The host cache has additional counters to track errors that do apply to specific IP addresses.
- The host cache size now is configurable using the host_cache_size system variable. This variable also controls the maximum size of the host_cache table because that table is the cache visible representation. Setting the size to 0 disables the host cache. This is similar to disabling the cache by starting the server with --skip-host-cache, but using host_cache_size is more flexible because it can also be used to resize, enable, and disable the host cache at runtime, not just at server startup. If you start the server with --skip-host-cache, the host cache cannot be re-enabled at runtime.
- New Connection_errors_xxx status variables provide information about connection errors that do not apply to specific client IP addresses.
For more information, see DNS Lookups and the Host Cache, and The host_cache Table. (Bug #22821, Bug #24906, Bug #45817, Bug #59404, Bug #11746048, Bug #11746269, Bug #11754244, Bug #11766316)

Optimizer Notes

Reporting of how to sort a result set in EXPLAIN has been improved for some statements. This sorting decision could be reported incorrectly, causing Using filesort or Using temporary to be reported when they should not have been or vice versa. This could occur for statements that included index hints, that had the form SELECT SQL_BIG_RESULT ... GROUP BY, that used SQL_CALC_FOUND_ROWS with LIMIT, or that used GROUP BY, ORDER BY, and LIMIT. (Bug #11744768, Bug #1560)
These query optimizer improvements were implemented:
- The EXPLAIN statement now can produce output in JSON format. To select this, use EXPLAIN FORMAT = JSON explainable_stmt syntax. With FORMAT = JSON, the output includes regular EXPLAIN information, as well as extended and partition information.
  
  Traditional EXPLAIN output has also changed so that empty columns contain NULL rather the empty string. In addition, UNION RESULT rows have Using filesort in the Extra column because a temporary table is used to buffer UNION results.
  
  To work for both Optimizer Trace and JSON-format EXPLAIN output, the end_marker parameter for the optimizer_trace system variable has been moved to a separate end_markers_in_json system variable. This is an incompatible change to the optimizer_trace variable. For more information, see MySQL Internals: Tracing the Optimizer.
- The optimizer tries to find the best query execution plan by beginning with the most promising table and recursively adding to the plan the most promising of the remaining tables. Partial execution plans with a higher cost than an already found plan are pruned. The optimizer now attempts to improve the order in which it adds tables to the plan, resulting in a reduction of the number of partial plans considered.
  
  Queries that are likely to have improved performance are joins of many tables, where most tables use eq_ref or ref join types (as indicated by EXPLAIN output).
  
  A new status variable, Last_query_partial_plans, counts the number of iterations the optimizer makes in execution plan construction for the previous query.
- The optimizer uses semijoin and materialization strategies to optimize subquery execution. See Optimizing Subqueries with Semijoin Transformations, and Optimizing Subqueries with Materialization. In addition, the Batched Key Access (BKA) Join and Block Nested-Loop (BNL) Join algorithms used for inner join and outer join operations have been extended to support semijoin operations. For more information, see Block Nested-Loop and Batched Key Access Joins.
  
  Several flags have been added to the optimizer_switch system variable to enable control over semijoin and subquery materialization strategies. The semijoin flag controls whether semijoins are used. If it is set to on, the firstmatch and loosescan flags enable finer control over the permitted semijoin strategies. The materialization flag controls whether subquery materialization is used. If semijoin and materialization are both on, semijoins also use materialization where applicable. These flags are on by default. See Switchable Optimizations.
- For expressions such as col_name IN(values) that compare a column to a list of values, the optimizer previously made row estimates using index dives for each value in the list. This becomes inefficient as the number of values becomes large. The optimizer now can make row estimates for such expressions using index statistics instead, which is less accurate but quicker for a large number of values. The point at which the optimizer switches from index dives to index statistics is configurable using the new eq_range_index_dive_limit system variable. For more information, see Equality Range Optimization of Many-Valued Comparisons.

Performance Schema Notes

The Performance Schema has these additions:
- The Performance Schema now has a host_cache table that exposes the contents of the host cache so that it can be examined using SELECT statements. See Host Cache Notes elsewhere in this changelog.
- The Performance Schema now maintains statement digest information. This normalizes and groups statements with the same “signature” and permits questions to be answered about the types of statements the server is executing and how often they occur.
  - A statement_digest consumer in the setup_consumers table controls whether the Performance Schema maintains digest information.
  - The statement event tables (events_statements_current, events_statements_history, and events_statements_history_long) have DIGEST and DIGEST_TEXT columns that contain digest MD5 values and the corresponding normalized statement text strings.
  - A events_statements_summary_by_digest table provides aggregated statement digest information.
For more information, see The host_cache Table, Performance Schema Statement Event Tables, and Statement Summary Tables.

If you upgrade to this MySQL release from an earlier version, you must run mysql_upgrade (and restart the server) to incorporate these changes into the performance_schema database.

Security Notes

Passwords stored in the older hash format used before MySQL 4.1 are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords and the mysql_old_password authentication plugin are now deprecated. To prevent connections using accounts that have pre-4.1 password hashes, the secure_auth system variable is now enabled by default. (To permit connections for accounts that have such password hashes, start the server with --secure_auth=0.) (Bug #13586336)
MySQL client programs now issue a warning if a password is given on the command line that this can be insecure.

Functionality Added or Changed

Incompatible Change: The obsolete OPTION modifier for the SET statement has been removed.
InnoDB: --ignore-builtin-innodb is now ignored if used. (Bug #13586262)
OS X; Microsoft Windows: A new CMake option, MYSQL_PROJECT_NAME, can be set on Windows or OS X to be used in the project name. (Bug #13551687)
Microsoft Windows: A new server option, --slow-start-timeout, controls the Windows service control manager's service start timeout. The value is the maximum number of milliseconds that the service control manager waits before trying to kill the MySQL service during startup. The default value is 15000 (15 seconds). If the MySQL service takes too long to start, you may need to increase this value. A value of 0 means there is no timeout. (Bug #45546, Bug #11754011)
The MySQL-shared-compat RPM package enables users of Red Hat-provided mysql-*-5.1 RPM packages to migrate to Oracle-provided MySQL-*-5.5 packages. MySQL-shared-compat now replaces the Red Hat mysql-libs package by replacing libmysqlclient.so files of the latter package, thus satisfying dependencies of other packages on mysql-libs. This change affects only users of Red Hat (or Red Hat-compatible) RPM packages. Nothing is different for users of Oracle RPM packages. (Bug #13867506)
Temporary tables for INFORMATION_SCHEMA queries now use dynamic MyISAM row format if they contain sufficiently large VARCHAR columns, resulting in space savings. (Bug #13627632)
As of MySQL 5.5.3, the LOW_PRIORITY modifier for LOCK TABLES ... LOW_PRIORITY WRITE has no effect. This modifier is now deprecated. Its use should be avoided and now produces a warning. Use LOCK TABLES ... WRITE instead. (Bug #13586314)
If the log_queries_not_using_indexes system variable is enabled, slow queries that do not use indexes are written to the slow query log. In this case, it is now possible to put a logging rate limit on these queries by setting the new log_throttle_queries_not_using_indexes system variable, so that the slow query log does not grow too quickly. By default, this variable is 0, which means there is no limit. Positive values impose a per-minute limit on logging of queries that do not use indexes. The first such query opens a 60-second window within which the server logs queries up to the given limit, then suppresses additional queries. If there are suppressed queries when the window ends, the server logs a summary that indicates how many there were and the aggregate time spent in them. The next 60-second window begins when the server logs the next query that does not use indexes. (Bug #55323, Bug #11762697)
Several subquery performance issues were resolved through the implementation of semijoin subquery optimization strategies. See Optimizing Subqueries with Semijoin Transformations. (Bug #47914, Bug #11756048, Bug #58660, Bug #11765671, Bug #10815, Bug #11745162, Bug #9021, Bug #13519134, Bug #48763, Bug #11756798, Bug #25130, Bug #11746289)
The mysql client now supports an --init-command=str option. The option value is an SQL statement to execute after connecting to the server. If auto-reconnect is enabled, the statement is executed again after reconnection occurs. (Bug #45634, Bug #11754087)
New utf8_general_mysql500_ci and ucs2_general_mysql500_ci collations have been added that preserve the behavior of utf8_general_ci and ucs2_general_ci from versions of MySQL previous to 5.1.24. Bug #27877 corrected an error in the original collations but introduced an incompatibility for columns that contain German 'ß' LATIN SMALL LETTER SHARP S. (As a result of the fix, that character compares equal to characters with which it previously compared different.) A symptom of the problem after upgrading to MySQL 5.1.24 or newer from a version older than 5.1.24 is that CHECK TABLE produces this error:
```
Table upgrade required.
Please do "REPAIR TABLE `t`" or dump/reload to fix it!
```
Unfortunately, REPAIR TABLE could not fix the problem. The new collations permit older tables created before MySQL 5.1.24 to be upgraded to current versions of MySQL.

To convert an affected table after a binary upgrade that leaves the table files in place, alter the table to use the new collation. Suppose that the table t1 contains one or more problematic utf8 columns. To convert the table at the table level, use a statement like this:
```
ALTER TABLE t1
CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_mysql500_ci;
```
To apply the change on a column-specific basis, use a statement like this (be sure to repeat the column definition as originally specified except for the COLLATE clause):
```
ALTER TABLE t1
MODIFY c1 CHAR(N) CHARACTER SET utf8 COLLATE utf8_general_mysql500_ci;
```
To upgrade the table using a dump and reload procedure, dump the table using mysqldump, modify the CREATE TABLE statement in the dump file to use the new collation, and reload the table.

After making the appropriate changes, CHECK TABLE should report no error. (Bug #43593, Bug #11752408)

References: See also: Bug #27877.
The SET TRANSACTION and START TRANSACTION statements now support READ WRITE and READ ONLY modifiers to set the transaction access mode for tables used in transactions. The default mode is read/write, which is the same mode as previously. Read/write mode now may be specified explicitly with the READ WRITE modifier. Using READ ONLY prohibits table changes and may enable storage engines to make performance improvements that are possible when changes are not permitted.

In addition, the new --transaction-read-only option and tx_read_only system variable permit the default transaction access mode to be set at server startup and runtime.

For more information, see SET TRANSACTION Statement, and START TRANSACTION, COMMIT, and ROLLBACK Statements.
MySQL distributions no longer include the GPL readline input-editing library. This results in simpler maintenance and support, and simplifies licensing considerations.

Bugs Fixed

Incompatible Change; Replication: CHANGE MASTER TO statements were written into the error log using quoted numeric values, although the syntax for this statement does not allow such option values to be quoted. This meant that such statements could not be copied from the error log and re-run verbatim. Now CHANGE MASTER TO statements are written to the error log without the extraneous quotation marks, and so are syntactically correct as logged.
Incompatible Change: A change in MySQL 5.6.3 caused LAST_DAY() to be more strict and reject incomplete dates with a day part of zero. For this function, a nonzero day part is not necessary, so the change has been reverted. (Bug #13458237)
Important Change; InnoDB: When a row grew in size due to an UPDATE operation, other (non-updated) columns could be moved to off-page storage so that information about the row still fit within the constraints of the InnoDB page size. The pointer to the new allocated off-page data was not set up until the pages were allocated and written, potentially leading to lost data if the system crashed while the column was being moved out of the page. The problem was more common with tables using ROW_FORMAT=DYNAMIC or ROW_FORMAT=COMPRESSED along with the Barracuda file format, particularly with the innodb_file_per_table setting enabled, because page allocation operations are more common as the .ibd tablespace files are extended. Still, the problem could occur with any combination of InnoDB version, file format, and row format.

A related issue was that during such an UPDATE operation, or an INSERT operation that reused a delete-marked record, other transactions could see invalid data for the affected column, regardless of isolation level.

The fix corrects the order of operations for moving the column data off the original page and replacing it with a pointer. Now if a crash occurs at the precise moment when the column data is being transferred, the transfer will not be re-run during crash recovery.

In MySQL 5.1, this fix applies to the InnoDB Plugin, but not the built-in InnoDB storage engine. (Bug #13721257, Bug #12612184, Bug #12704861)
Important Change; Partitioning: The query cache did not always function correctly with partitioned tables in a transactional context. For this reason, the query cache is now disabled for any queries using partitioned tables, and such queries can no longer be cached. For more information, see Restrictions and Limitations on Partitioning. (Bug #11761296, Bug #53775)
Important Change; Replication: The CHANGE MASTER TO statement was not checked for invalid characters in values for options such as MASTER_HOST and MASTER_USER. In addition, when the server was restarted, a value containing certain characters was trimmed, causing the loss of its original value. Now such values are validated, and in cases where the value contains invalid characters, including linefeed (\n or 0x0A) characters, the statement fails with an error (ER_MASTER_INFO). (Bug #11758581, Bug #50801)
Important Change; Replication: Moving the binary log file, relay log file, or both files to a new location, then restarting the server with a new value for --log-bin, --relay-log, or both, caused the server to abort on start. This was because the entries in the index file overrode the new location. In addition, paths were calculated relative to datadir (rather than to the --log-bin or --relay-log values).

The fix for this problem means that, when the server reads an entry from the index file, it now checks whether the entry contains a relative path. If it does, the relative part of the path is replaced with the absolute path set using the --log-bin or --relay-log option. An absolute path remains unchanged; in such a case, the index must be edited manually to enable the new path or paths to be used. (Bug #11745230, Bug #12133)
Performance; InnoDB: The optimizer now takes into account InnoDB page sizes other than 16KB, which can be configured with the innodb_page_size option when creating a MySQL instance. This change improves the estimates of I/O costs for queries on systems with non-default InnoDB page sizes. (Bug #13623078)
Performance; InnoDB: Memory allocation for InnoDB tables was reorganized to reduce the memory overhead for large numbers of tables or partitions, avoiding situations where the “resident set size” could grow regardless of FLUSH TABLES statements. The problem was most evident for tables with large row size. Some of the memory that was formerly allocated for every open table is now allocated only when the table is modified for the first time. (Bug #11764622, Bug #57480)
Performance: Temporary MyISAM tables (unlike normal MyISAM tables) did not use the dynamic row format when they contained VARCHAR columns, resulting in larger temporary files (and more file I/O) than necessary. Dynamic row format now is used, which results in smaller tables that are faster to process. (Bug #13350136, Bug #78840, Bug #22023218)
InnoDB: An erroneous assertion could occur, in debug builds only, when creating an index on a column containing zero-length values (that is, ''). (Bug #13654923)
InnoDB: A DDL operation such as ALTER TABLE ... ADD COLUMN could stall, eventually timing out with an Error 1005: Can't create table message referring to fil_rename_tablespace. (Bug #13636122, Bug #62100, Bug #63553)
InnoDB: If InnoDB was started with innodb_force_recovery set to a value of 3 or 4, and there are transactions to roll back, normal shutdown would hang waiting for those transactions to complete. Now the shutdown happens immediately, without rolling back any transactions, because nonzero values for innodb_force_recovery are only appropriate for troubleshooting and diagnostic purposes. (Bug #13628420)
InnoDB: The MySQL server could hang in some cases if the configuration option innodb_use_native_aio was turned off. (Bug #13619598)
InnoDB: A Valgrind error was fixed in the function os_aio_init(). (Bug #13612811)
InnoDB: The configuration option innodb_sort_buf_size was renamed to innodb_sort_buffer_size for consistency. This work area is used while creating an InnoDB index. (Bug #13610358)
InnoDB: The server could crash when creating an InnoDB temporary table under Linux, if the $TMPDIR setting points to a tmpfs filesystem and innodb_use_native_aio is enabled, as it is by default in MySQL 5.5.4 and higher. The entry in the error log looked like:
```
101123  2:10:59  InnoDB: Operating system error number 22 in a file operation.
InnoDB: Error number 22 means 'Invalid argument'.
```
The crash occurred because asynchronous I/O is not supported on tmpfs in some Linux kernel versions. The workaround was to turn off the innodb_use_native_aio setting or use a different temporary directory. The fix causes InnoDB to turn off the innodb_use_native_aio setting automatically if it detects that the temporary file directory does not support asynchronous I/O. (Bug #13593888, Bug #11765450, Bug #58421)
InnoDB: During startup, the status variable Innodb_buffer_pool_dump_status could be empty for a brief time before being initialized to the correct value not started. (Bug #13513676)
InnoDB: Valgrind errors when referencing the internal function buf_LRU_scan_and_free_block() were fixed. (Bug #13491704)
InnoDB: The MySQL error log could contain messages like:
```
InnoDB: Ignoring strange row from mysql.innodb_index_stats WHERE ...
```
The fix makes the contents of the innodb_index_stats and innodb_table_stats tables case-sensitive, to properly distinguish the statistics for tables whose names differ only in lettercase. Other cases were fixed where the wrong name could be selected for an index while retrieving persistent statistics. (Bug #13432465)
InnoDB: References to C preprocessor symbols and macros HAVE_purify, UNIV_INIT_MEM_TO_ZERO, and UNIV_SET_MEM_TO_ZERO were removed from the InnoDB source code. They were only used in debug builds instrumented for Valgrind. They are replaced by calls to the UNIV_MEM_INVALID() macro. (Bug #13418934)
InnoDB: The MySQL server could halt with an assertion error:
```
InnoDB: Failing assertion: page_get_n_recs(page) > 1
```
Subsequent restarts could fail with the same error. The error occurred during a purge operation involving the InnoDB change buffer. The workaround was to set the configuration option innodb_change_buffering=inserts. (Bug #13413535, Bug #61104)
InnoDB: A discrepancy could arise between the number of available InnoDB undo logs and the number of undo logs that were currently active. Now the innodb_undo_logs system variable reports the number of active undo logs, and the new Innodb_available_undo_logs status variable reports the total number of undo logs. (Bug #13255225)
InnoDB: When doing a live downgrade from MySQL 5.6.4 or later, with innodb_page_size set to a value other than 16384, now the earlier MySQL version reports that the page size is incompatible with the older version, rather than crashing or displaying a “corruption” error. (Bug #13116225)
InnoDB: Certain CREATE TABLE statements could fail for InnoDB child tables containing foreign key definitions. This problem affected Windows systems only, with the setting lower_case_table_names=0. It was a regression from MySQL bug #55222. (Bug #13083023, Bug #60229)
InnoDB: If the server crashed during a TRUNCATE TABLE or CREATE INDEX statement for an InnoDB table, or a DROP DATABASE statement for a database containing InnoDB tables, an index could be corrupted, causing an error message when accessing the table after restart:
```
InnoDB: Error: trying to load index index_name for table table_name
InnoDB: but the index tree has been freed!
```
In MySQL 5.1, this fix applies to the InnoDB Plugin, but not the built-in InnoDB storage engine. (Bug #12861864, Bug #11766019)
InnoDB: A DDL operation for an InnoDB table could cause a busy MySQL server to halt with an assertion error:
```
InnoDB: Failing assertion: trx->error_state == DB_SUCCESS
```
The error occurred if the DDL operation was run while all 1023 undo slots were in use by concurrent transactions. This error was less likely to occur in MySQL 5.5 and 5.6, because raising the number of InnoDB undo slots increased the number of simultaneous transactions (corresponding to the number of undo slots) from 1K to 128K. (Bug #12739098, Bug #62401)
InnoDB: InnoDB persistent statistics gave less accurate estimates for date columns than for columns of other data types. The fix changes the way cardinality is estimated for nonunique keys, and avoids situations where identical values could be counted twice if they occurred on different index pages. (Bug #12429443)
InnoDB: The innodb_max_purge_lag variable controls how to delay DML operations when purge operations are lagging. Previously, if an old consistent read view was detected, DML operations would not be delayed even though the purge lag exceeded the innodb_max_purge_lag setting.

Additionally, if the innodb_max_purge_lag setting was used, situations could arise in which the DML delay time would continue to increase but not be applied right away due to the presence an old consistent read view. This could result in a lengthy DML delay when the accumulated DML delay time is eventually applied.

This fix caps the DML delay at a maximum value, removes the consistent read check, and revises the DML delay calculation. (Bug #12407434, Bug #60776)
InnoDB: With 1024 concurrent InnoDB transactions running concurrently and the innodb_file_per_table setting enabled, a CREATE TABLE operation for an InnoDB table could fail. The .ibd file from the failed CREATE TABLE was left behind, preventing the table from being created later, after the load had dropped.

The fix adds error handling to delete the erroneous .ibd file. This error was less likely to occur in MySQL 5.5 and 5.6, because raising the number of InnoDB undo slots increased the number of simultaneous transactions needed to trigger the bug, from 1K to 128K. (Bug #12400341)
InnoDB: Improved the accuracy of persistent InnoDB statistics for large tables. The estimate of distinct records could be inaccurate if the index tree was more than 3 levels deep. (Bug #12316365)
InnoDB: Shutdown could hang with messages like this in the log:
```
Waiting for purge thread  to be suspended
```
After 1 hour, the shutdown times out and mysqld quits. This problem is most likely to occur with a high value for innodb_purge_threads. (Bug #11765863, Bug #58868, Bug #60939)
InnoDB: When DROP TABLE failed due to all undo slots being in use, the error returned was Unknown table '...' rather than the expected Too many active concurrent transactions. (Bug #11764724, Bug #57586)

References: See also: Bug #11764668, Bug #57529.

InnoDB: Server startup could produce an error for temporary tables using the InnoDB storage engine, if the path in the $TMPDIR variable ended with a / character. The error log would look like:

120202 19:21:26  InnoDB: Operating system error number 2 in a file operation.
InnoDB: The error means the system cannot find the path specified.
InnoDB: If you are installing InnoDB, remember that you must create
InnoDB: directories yourself, InnoDB does not create them.
120202 19:21:26  InnoDB: Error: trying to open a table, but could not
InnoDB: open the tablespace file './t/#sql7750_1_0.ibd'!
InnoDB: Have you moved InnoDB .ibd files around without using the
InnoDB: commands DISCARD TABLESPACE and IMPORT TABLESPACE?
InnoDB: It is also possible that this is a temporary table #sql...,
InnoDB: and MySQL removed the .ibd file for this.

The workaround for the problem was to create a similar temporary table again, copy its .frm file to tmpdir under the name mentioned in the error message (for example, #sql123.frm) and restart mysqld with tmpdir set to its normal value without a trailing slash, for example /var/tmp. On startup, MySQL would see the .frm file and issue DROP TABLE for the orphaned temporary table. (Bug #11754376, Bug #45976)

Partitioning: When creating a view from a SELECT statement that used explicit partition selection, the partition selection portion of the query was ignored. (Bug #13559657)
Partitioning: Adding a partition to an already existing LIST-partitioned table did not work correctly if the number of items in the new partition was greater than 16. This could happen when trying to add a partition using an ALTER TABLE ... ADD PARTITION statement, or an ALTER TABLE ... REORGANIZE PARTITION statement.

This 16-item limit was not apparent when using either CREATE TABLE ... PARTITION BY LIST or ALTER TABLE ... PARTITION BY LIST. (Bug #13029508, Bug #62505)
Partitioning: A function internal to the code for finding matching subpartitions represented an unsigned number as signed, with the result that matching subpartitions were sometimes missed in results of queries. (Bug #12725206, Bug #61765)

References: See also: Bug #20257.
Partitioning: An ALTER TABLE ... ADD PARTITION statement subsequent to ALTER TABLE ... REORGANIZE PARTITION failed on a table partitioned by HASH or KEY. (Bug #11764110, Bug #56909)
Replication: Executing mysqlbinlog with the --start-position=N option, where N was equal either to 0 or to a value greater than the length of the dump file, caused it to crash.

This issue was introduced in MySQL 5.5.18 by the fix for Bug #32228 and Bug #11747416. (Bug #13593869, Bug #64035)

References: This issue is a regression of: Bug #32228, Bug #11747416.
Replication: When starting the server, replication repositories were checked even when the server_id system variable was equal to 0 (the default), in spite of the fact that a valid nonzero value for server_id must be supplied for a server that acts as either a master or a slave in MySQL replication.

This could cause problems when trying to perform a live upgrade from MySQL 5.5, although it was possible to work around the issue by starting the server with --skip-slave-start (in addition to any other required options).

To avoid this problem, replication repositories are now checked only when the server is started with --server-id using a nonzero value. (Bug #13427444, Bug #13504821)
Replication: Formerly, the default value shown for the Port column in the output of SHOW SLAVE HOSTS was 3306 whether the port had been set incorrectly or not set at all. Now, when the slave port is not set, the actual port used by the slave is shown. This change also affects the default shown for the --report-port server option. (Bug #13333431)
Replication: A race condition could occur when running multiple instances of mysqld on a single machine, when more than slave thread was started at the same time, and each such thread tried to use the same temporary file concurrently. (Bug #12844302, Bug #62055)
Replication: It was possible on replication slaves where FEDERATED tables were in use to get timeouts on long-running operations, such as Error 1160 Got an error writing communication packets. The FEDERATED tables did not need to be replicated for the issue to occur. (Bug #11758931, Bug #51196)

References: See also: Bug #12896628, Bug #61790.
Replication: Statements that wrote to tables with AUTO_INCREMENT columns based on an unordered SELECT from another table could lead to the master and the slave going out of sync, as the order in which the rows are retrieved from the table may differ between them. Such statements include any INSERT ... SELECT, REPLACE ... SELECT, or CREATE TABLE ... SELECT statement. Such statements are now marked as unsafe for statement-based replication, which causes the execution of one to throw a warning, and forces the statement to be logged using the row-based format if the logging format is MIXED. (Bug #11758263, Bug #50440)
Replication: On Windows replication slave hosts, STOP SLAVE took an excessive length of time to complete when the master was down. (Bug #11752315, Bug #43460)
Replication: mysqlbinlog --database=dbname included all SET INSERT_ID=n assignments from the binary log in its output, even if database dbname was never referenced in the binary log. This was due to the fact that COMMIT statements were not associated with any database in the binary log. Now in such cases, the current database is tracked so that only those SET INSERT_ID assignments that are made in the context of changes to tables in database dbname are actually printed in the mysqlbinlog output. (Bug #11746146, Bug #23894)

References: See also: Bug #23890, Bug #46998, Bug #11761686, Bug #54201, Bug #11754117, Bug #45670.
Microsoft Windows: On Windows, rebuilds in a source distribution failed to create the initial database due to insufficient cleanup from the previous run or failure to find the proper server executable. (Bug #13431251)
Microsoft Windows: On Windows, the server incorrectly constructed the full path name of the plugin binary for INSTALL PLUGIN and CREATE FUNCTION ... SONAME. (Bug #45549, Bug #11754014)
mysqldump tried to execute SET statements as SET OPTION, which failed when used against 5.6 or higher servers because the deprecated OPTION keyword has been removed from SET syntax. (Bug #13813473)
The optimizer did not perform constant propagation for views, so a query containing views resulted in a less efficient execution plan than the corresponding query using only base tables. (Bug #13783777)
A memory leak could occur for queries containing a subquery that used GROUP BY on an outer column. (Bug #13724099)
After using an ALTER TABLE statement to change the KEY_BLOCK_SIZE property for an InnoDB table, for example when switching from an uncompressed to a compressed table, subsequent server restarts could fail with a message like:
```
InnoDB: Error: data file path/ibdata2 uses page size 1024,
InnoDB: but the only supported page size in this release is=16384
```
This issue is a regression introduced in MySQL 5.5.20. (Bug #13698765, Bug #64160)
In debug builds, a Debug Sync timeout warning was treated as an error, causing an assertion to be raised. (Bug #13688248)
_mi_print_key() iterated one time too many when there was a NULL bit, resulting in Valgrind warnings. (Bug #13686970)
Pushing down to InnoDB an index condition that called a stored function resulted in a server crash. This kind of condition is no longer pushed down. (Bug #13655397)
A SELECT from a subquery that returned an empty result could itself fail to return an empty result as expected. (Bug #13651009, Bug #13650418)
For debug builds, negative values with a zero integer part and nonzero fractional part (such as -0.1111) were not detected, so the negative fractional part was later cast to a large unsigned number and raised an assertion. (Bug #13616434)
If during server startup a signal such as SIGHUP was caught prior to full server initialization, the server could crash. This was due to a race condition between the signal handler thread and the main thread performing server initialization. To prevent this from happening, signal processing is now suspended until full initialization of all server subsystems has been completed successfully. (Bug #13608371, Bug #62311)
The shared version of libmysqlclient did not export these functions for linking by client programs: get_tty_password(), handle_options(), my_print_help(). (Bug #13604121)
An aggregated expression of type MIN() or MAX() should return NULL but could instead return the empty set if the query was implicitly grouped and there was no HAVING clause that evaluates to FALSE. (Bug #13599013)
Left join queries could be incorrectly converted to inner joins and return erroneous result sets. (Bug #13595212)
Date-handling code could raise an assertion attempting to calculate the number of seconds since the epoch. (Bug #13545236)
For queries that used a join type of ref_or_null, the optimizer could skip the filesort operation and sort the results incorrectly. (Bug #13531865)
For some queries, a filesort operation was done even when the result contained only a single row and needed no sorting. (Bug #13529048)
The optimizer could return an incorrect select limit in some cases when a query included no explicit LIMIT clause. (Bug #13528826)
In some cases, the optimizer failed to use a covering index when that was possible and read data rows instead. (Bug #13514959)
SELECT statements failed for the EXAMPLE storage engine. (Bug #13511529)

References: This issue is a regression of: Bug #11746275.
The Performance Schema instrumentation for stages did not fully honor the ENABLED column in the schema.setup_instruments table. (Bug #13509513)
Converting a string ending with a decimal point (such as '1.') to a floating-point number raised a data truncation warning. (Bug #13500371)
Use of an uninitialized TABLE_SHARE member could cause a server crash. (Bug #13489996)
Some outer joins that used views as inner tables did not evaluate conditions correctly. (Bug #13464334)
A query that used an index on a CHAR column referenced in a BETWEEN clause could return invalid results. (Bug #13463488, Bug #63437)
Expressions that compared a BIGINT column with any non-integer constant were performed using integers rather than decimal or float values, with the result that the constant could be truncated. This could lead to any such comparison that used <, >, <=, >=, =, !=/<>, IN, or BETWEEN yielding false positive or negative results. (Bug #13463415, Bug #11758543, Bug #63502, Bug #50756)
An application linked against libmysqld could crash in debug mode with a stack smashing detected error if it tried to connect without specifying the user name. (Bug #13460909)
Instantiating a derived table for a query with an empty result caused a server crash. (Bug #13457552)
When the optimizer performed conversion of DECIMAL values while evaluating range conditions, it could produce incorrect results. (Bug #13453382)
Implicitly grouped queries with a const table and no matching rows could return incorrect results. (Bug #13430588)
For debug builds, enabling optimizer_trace could cause an assertion to be raised. (Bug #13430443)
Enabling index condition pushdown could cause performance degradation. (Bug #13430436)
When a fixed-width row was inserted into a MyISAM temporary table, the entire content of the record buffer was written to the table, including any trailing space contained in VARCHAR columns, the issue being that this trailing space could be uninitialized. This problem has been resolved by insuring that only the bytes actually used to store the VARCHAR (and none extra) are copied and inserted in such cases. (Bug #13389854, Bug #79028, Bug #22123583)
Fractional seconds parts were lost for certain UNION ALL queries. (Bug #13375823)
When merging ranges that effectively resulted in a full index scan, the optimizer did not discard the range predicate as unneeded. (Bug #13354910)
When executing EXPLAIN, it was assumed that only the default multi-range read implementation could produce an ordered result; this meant that when a query on a table that used a storage engine providing its own sorted MRR, it was ignored, so that EXPLAIN failed to report Using MRR even when a multi-range read was used. (Bug #13330645)
Some multiple-table updates could update a row twice. (Bug #13095459)
Performance Schema idle event timings were not normalized to the same units as wait timings. (Bug #13018537)
In MySQL 5.6.3, a number of status variables were changed to longlong types so that they would roll over much later. However, the format string used by mysqladmin status to print Queries per second values did not reflect this, causing such values to be misreported. (Bug #12990746)

References: See also: Bug #42698. This issue is a regression of: Bug #11751727.
For debug builds, two assertions could be raised erroneously for UPDATE statements. (Bug #12912171)
When the result of a stored function returning a non-integer type was evaluated for NULL, an incorrect type warning (Warning 1292 Truncated incorrect INTEGER value) is generated, although such a test for NULL should work with any type. This could cause stored routines not handling the warning correctly to fail.

The issue could be worked around by wrapping the result in an expression, using a function such as CONCAT(). (Bug #12872824, Bug #62125)
When running mysqldump with both the --single-transaction and --flush-logs options, the flushing of the log performed an implicit COMMIT (see Statements That Cause an Implicit Commit), causing more than one transaction to be used and thus breaking consistency. (Bug #12809202, Bug #61854)
A query that used an aggregate function such as MAX() or MIN() of an index with NOT BETWEEN in the WHERE clause could fail to match rows, thus returning an invalid result. (Bug #12773464, Bug #61925)
With ONLY_FULL_GROUP_BY SQL mode enabled, columns that were not aggregated in the select list or named in a GROUP BY were incorrectly permitted in ORDER BY. (Bug #12626418)
Mishandling of NO_BACKSLASH_ESCAPES SQL mode within stored procedures on slave servers could cause replication failures. (Bug #12601974)
Passing a user variable as an argument to GROUP_CONCAT() could cause a server exit if the variable value changed during query execution. (Bug #12408412)
LOAD INDEX INTO CACHE could cause a server exit if the index cache was too small. (Bug #12361113)
With ONLY_FULL_GROUP_BY SQL mode enabled, a query that uses GROUP BY on a column derived from a subquery in the FROM clause failed with a column isn't in GROUP BY error, if the query was in a view. (Bug #11923239)
Attempting to execute ALTER TABLE on a temporary MERGE table having an underlying temporary table rendered the MERGE table unusable, unless the ALTER TABLE specified a new list of underlying tables. (Bug #11764786, Bug #57657)
It was possible in the event of successive failures for mysqld_safe to restart quickly enough to consume excessive amounts of CPU. Now, on systems that support the sleep and date system utilities, mysqld_safe checks to see whether it has restarted more than 5 times in the current second, and if so, waits 1 second before attempting another restart. (Bug #11761530, Bug #54035)
A HAVING clause in a query using MIN() or MAX() was sometimes ignored. (Bug #11760517, Bug #52935)

References: See also: Bug #11758970, Bug #51242, Bug #11759718, Bug #52051.
When used with the --xml option, mysqldump --routines failed to dump any stored routines, triggers, or events. (Bug #11760384, Bug #52792)
If an attempt to initiate a statement failed, the issue could not be reported to the client because it was not prepared to receive any error messages prior to the execution of any statement. Since the user could not execute any queries, they were simply disconnected without providing a clear error.

After the fix for this issue, the client is prepared for an error as soon as it attempts to initiate a statement, so that the error can be reported prior to disconnecting the user. (Bug #11755281, Bug #47032)
Previously, .OLD files were not included among the files deleted by DROP DATABASE. Files with this extension are now also deleted by the statement. (Bug #11751736, Bug #42708)
A prepared statement using a view whose definition changed between preparation and execution continued to use the old definition, which could cause the prepared statement to return incorrect results. (Bug #11748352, Bug #36002)
Some debugging information was written to the buffer after a flush, resulting in the information not appearing until the next flush. (Bug #64048, Bug #13608112)
Locale information for FORMAT() function instances was lost in view definitions. (Bug #63020, Bug #13344643)
mysqlhotcopy failed for databases containing views. (Bug #62472, Bug #13006947, Bug #12992993)
The VIO description string was initialized even for connections where it was unneeded. (Bug #62285, Bug #12951586)
On Windows, pasting multiple-line input including a CRLF terminator on the last line into the mysql client resulted in the first character of the last line being changed, resulting in erroneous statements. Handling of newlines in pasted input was also incorrect. (Bug #60901, Bug #12589167, Bug #64104, Bug #13639107)
The contents of the shared and shared-compat RPM packages had been changed in versions 5.5.6 and 5.6.1 to avoid the overlap which they traditionally had (and still have in MySQL 5.0 and 5.1). However, the RPM meta information had not been changed in accordance, and so RPM still assumed a conflict between shared and shared-compat RPM packages. This has been fixed. (Bug #60855, Bug #12368215)

References: See also: Bug #56150.
The result of SUBSTRING_INDEX() could be missing characters when used as an argument to conversion functions such as LOWER(). (Bug #60166, Bug #11829861)
UPDATE IGNORE returned an incorrect count for number of rows updated when there were duplicate-key conflicts in a multiple-table update. (Bug #59715, Bug #11766576)
The optimizer mishandled STRAIGHT_JOIN used with nested joins; for example, by not evaluating tables in the specified order. (Bug #59487, Bug #11766384, Bug #43368, Bug #11752239, Bug #60080, Bug #11766858)
A subquery involved in a comparison requiring a character set conversion caused an error that resulted in a server crash. (Bug #59185, Bug #11766143)
The embedded server crashed when argc = 0. (Bug #57931, Bug #12561297)
If tables were locked by LOCK TABLES ... READ in another session, SET GLOBAL read_only = 1 failed to complete. (Bug #57612, Bug #11764747)
Invalid memory reads could occur when cmp_item_sort_string::store_value() tried to refer to a temporary value that could be changed or deleted by other functions. (Bug #57510, Bug #11764651)
Assigning the result of a subquery to a user variable raised an assertion when the outer query included DISTINCT and GROUP BY. (Bug #57196, Bug #11764371)
For comparisons containing out-of-range constants, the optimizer permitted warnings to leak through to the client, even though it accounted for the range issue internally. (Bug #56962, Bug #11764155)
A confusing CREATE TABLE error message was improved. (Bug #54963, Bug #11762377)
The handle_segfault() signal-handler code in mysqld could itself crash due to calling unsafe functions. (Bug #54082, Bug #11761576)
Using myisamchk with the sort recover method to repair a table having fixed-width row format could cause the row pointer size to be reduced, effectively resulting in a smaller maximum data file size. (Bug #48848, Bug #11756869)
Enabling myisam_use_mmap could cause the server to crash. (Bug #48726, Bug #11756764)
For MEMORY tables, a scan of a HASH index on a VARCHAR column could fail to find some rows if the index was on a prefix of the column. (Bug #47704, Bug #11755870)
myisam_sort_buffer_size could not be set larger than 4GB on 64-bit systems. (Bug #45702, Bug #11754145)
The stored routine cache was subject to a small memory leak that over time or with many routines being used could result in out-of-memory errors.

The fix for this issue also introduces a new global server system variable stored_program_cache which can be used for controlling the size of the stored routine cache. (Bug #44585, Bug #11753187)
Under some circumstances, the result of SUBSTRING_INDEX() incorrectly depended on the contents of the previous row. (Bug #42404, Bug #11751514)
Setting an event to DISABLED status and with the ON COMPLETION NOT PRESERVE attribute caused it to be dropped at the next server restart. (Bug #37666, Bug #11748899)
Due to improper locking, concurrent inserts into an ARCHIVE table at the same time as repair and check operations on the table resulted in table corruption. (Bug #37280, Bug #11748748)
Stored functions could produce an error message that referred to ORDER BY even though the offending statement within the function had no such clause. (Bug #35410, Bug #11748187)

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