This release continues the process begun in MySQL 5.6.6 of making changes to the default values of server parameters. The motivation for these changes is to provide better out-of-box performance and to reduce the need for database administrators to change settings manually. These changes are subject to revision in future releases as we gain feedback.

In some cases, a parameter has a different fixed default value. In other cases, the server autosizes a parameter at startup using a formula based on other related parameters or server host configuration, rather than using a fixed value. For example, the setting for host_cache_size is its previous default of 128, adjusted up by an amount proportional to the value of max_connections. The idea behind autosizing is that when the server has information available to make a decision about a parameter setting likely to be better than a fixed default, it will.

The following table summarizes changes to defaults. For variables that are autosized, the main variable description provides additional detail about the sizing algorithm. See Server System Variables, and InnoDB Startup Options and System Variables. Any of these default settings can be overridden by specifying an explicit value at server startup.

On Unix platforms, mysql_install_db supports a new option, --random-passwords, that provides for more secure MySQL installation. Invoking mysql_install_db with --random-passwords causes it to perform the following actions in addition to its normal operation:

As a result of these actions, it is necessary after installation to start the server, connect as root using the password written to the .mysql_secret file, and to select a new root password. Until this is done, root cannot do anything else. This must be done for each root account you intend to use. To change the password, you can use the SET PASSWORD statement (for example, with the mysql client). You can also use mysqladmin or mysql_secure_installation.

New RPM install operations (not upgrades) invoke mysql_install_db with the --random-passwords option. As a consequence, RPM installs from this version onward will have their root accounts secured, and will have no anonymous-user accounts. (Install operations using RPMs for Unbreakable Linux Network are unaffected because they do not use mysql_install_db.)

For install operations using a binary .tar.gz distribution or a source distribution, you can invoke mysql_install_db with the --random-passwords option manually to make your MySQL installation more secure. This is recommended, particularly for sites with sensitive data.

mysql_install_db is now a Perl script and can be used on any system with Perl installed. Previously, it was a shell script and available only on Unix platforms.

In addition, mysql_install_db is more strict about the --datadir option value. Only the last component of the path name is created if it does not exist; the parent directory must already exist or an error occurs. Previously, it created any nonexistent directories in the path name.

On Unix platforms, mysql_install_db now creates a default option file named my.cnf in the base installation directory. This file is created from a template included in the distribution package named my-default.cnf. You can find the template in or under the base installation directory. When started using mysqld_safe, the server uses my.cnf file by default. If my.cnf already exists, mysql_install_db assumes it to be in use and writes a new file named my-new.cnf instead.

With one exception, the settings in the default option file are commented and have no effect. The exception is that the file changes the sql_mode system variable from its default of NO_ENGINE_SUBSTITUTION to also include STRICT_TRANS_TABLES:

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

This setting produces a server configuration that results in errors rather than warnings for bad data in operations that modify transactional tables. See Server SQL Modes.

The my-default.cnf template replaces the older sample option files (my-small.cnf, my-medium.cnf, and so forth), which are no longer distributed.

InnoDB: The InnoDB transportable tablespace feature was enhanced to allow ALTER TABLE ... IMPORT TABLESPACE to succeed in some cases where the corresponding .cfg file was not available. This enhancement allows recovery of data even in some cases where the system tablespace is corrupted or deleted. (Bug #14589582, Bug #66715)

The number of atomic operations performed by the Performance Schema was reduced. (Bug #14658739)

ALTER USER now can be used as a prepared statement. (Bug #66874, Bug #14646014)

On Unix systems, the mysql client writes statements executed interactively to a history file (see mysql Logging). mysql now ignores for logging purposes statements that match any pattern in the “ignore” list. By default, the pattern list is "*IDENTIFIED*:*PASSWORD*", to ignore statements that refer to passwords. Pattern matching is not case sensitive. Within patterns, two characters are special:

To specify additional patterns, use the --histignore command option or set the MYSQL_HISTIGNORE environment variable. (If both are specified, the option value takes precedence.) The value should be a colon-separated list of one or more patterns, which are appended to the default pattern list.

Patterns specified on the command line might need to be quoted or escaped to prevent your command interpreter from treating them specially. For example, to suppress logging for UPDATE and DELETE statements in addition to statements that refer to passwords, invoke mysql like this:

shell> mysql --histignore="*UPDATE*:*DELETE*"

(Bug #48287, Bug #11756377)

On Windows, many MySQL executables depend on the libeay32.dll and ssleay32.dll SSL libraries at runtime. To ensure that the proper versions of these libraries are found, the install process copies them into the same directory as the executables.

The SHOW AUTHORS and SHOW CONTRIBUTORS statements have been removed.

Important Change; Replication: When running the slave with the --slave-skip-errors option, successive skipped events (errors logged as warnings) were found to contain information from previous warnings, which caused an excessive amount of redundant information to be written to the error log. This problem could occur when using row-based or mixed-format binary logging.

The fix for this issue is to clear these warnings prior to processing the next skipped event. In addition, the skipped events are now handled in the same way regardless of the value of binlog_format, and a skipped error always causes a warning to be written to the error log, as long as the value of the log_warnings system variable is greater than 1. (Bug #12776842)

Important Change: The server system variables profiling, have_profiling, and profiling_history_size are now deprecated, and are subject to removal in a future release of the MySQL Server. (Bug #14658683)

InnoDB: The thread gathering persistent statistics for an InnoDB table could cause a serious error if it accessed the table while a TRUNCATE TABLE operation was in progress:

InnoDB: Assertion failure in thread thread_num in file fsp0fsp.cc line 1882 

(Bug #14765035)

InnoDB: When a CREATE INDEX operation failed for an InnoDB FULLTEXT index due to a duplicate key error, some allocated memory was not freed. (Bug #14759111)

InnoDB: During a brief time window while creating an InnoDB unique index, MySQL could print a spurious warning message:

WARNING: CANNOT FIND INDEX ?index_name IN INNODB INDEX TRANSLATION TABLE

The cause was that MySQL started enforcing the uniqueness constraint before the existence of the index was fully registered. The fix suppresses the incorrect message during this final stage of index creation. (Bug #14735988)

InnoDB: An online DDL operation to create a unique index could fail to detect duplicate index values, when the duplicate values were caused by DML operations while the index was being created. (Bug #14733674)

InnoDB: During an online DDL operation, a duplicate key error could be incorrectly issued if a record was inserted and subsequently updated while the table was being rebuilt. (Bug #14723456)

InnoDB: The auxiliary tables for FULLTEXT indexes were being created in the system tablespace, regardless of the setting for the innodb_file_per_table configuration option. (Bug #14723291)

InnoDB: When using the transportable tablespace feature, the ALTER TABLE ... IMPORT TABLESPACE statement could crash if the InnoDB table being flushed contained a FULLTEXT index. With this fix, the table data can be imported, although you must drop and re-create the FULLTEXT index after the import operation. (Bug #14712962, Bug #67081)

InnoDB: An assertion failure occurred when a bogus duplicate key error was flagged during online ALTER TABLE. This issue only occurred for a table that lacked a primary key and any secondary indexes. This patch fixes the assertion failure, but not the bogus duplicate key error, which is reported as Bug#14723456. (Bug #14712710)

InnoDB: The InnoDB memcached plugin can now work with tables where the underlying character set is multibyte. (Bug #14711015, Bug #67076)

InnoDB: If a CREATE TABLE statement failed due to a disk full error, some memory allocated during the operation was not freed properly. (Bug #14708715)

InnoDB: An ALTER TABLE operation on an InnoDB table containing a FULLTEXT index could cause make the server halt with an assertion error. The fix causes all ALTER TABLE operations for such tables to use the table-copying behavior of the ALGORITHM=COPY clause. (Bug #14681198)

InnoDB: If the server crashed while executing TRUNCATE TABLE for an InnoDB table containing a FULLTEXT index, further errors could occur during crash recovery, preventing the server from restarting. (Bug #14676345)

InnoDB: If an InnoDB table containing a FULLTEXT index was being modified by a TRUNCATE TABLE statement and on online DDL operation simultaneously, the server could end up with inconsistent internal locks or could crash. (Bug #14676329)

InnoDB: If creation of a FULLTEXT index failed because of a “row too large” condition, a subsequent ALTER TABLE operation could cause the server to halt with an error. (Bug #14668777)

InnoDB: If the MySQL server crashed while XA transactions were in PREPARED state, inconsistent data could be produced during crash recovery if the query cache was enabled. The fix allows MySQL to disable the query cache during crash recovery if required. (Bug #14658648)

InnoDB: MySQL could crash while creating an InnoDB table if the disk became full at a specific moment: after the .frm file was created but before the corresponding .ibd file was created. (Bug #14645935)

InnoDB: If the server crashed at the specific point when a change buffer entry was being merged into a buffer pool page, the transaction log and the change buffer were left in an inconsistent state. After a restart, MySQL could crash after reading the corresponding secondary index page. The problem was more likely to occur in MySQL 5.5 or later, where the original insert buffering mechanism was generalized to cover other operations. (Bug #14636528, Bug #66819, Bug #58571, Bug #61104, Bug #65443)

InnoDB: If a crash occurred during a CREATE TABLE operation, the InnoDB data dictionary could be left in an inconsistent state, causing a crash if the partially created table was accessed later. (Bug #14601290)

InnoDB: On startup, MySQL would not start if there was a mismatch between the value of the innodb_log_file_size configuration option and the actual size of the ib_logfile* files that make up the redo log. This behavior required manually removing the redo log files after changing the value of innodb_log_file_size. The fix causes MySQL to write all dirty pages to disk and re-create the redo log files during startup if it detects a size mismatch. (Bug #14596550)

InnoDB: With the innodb_file_per_table setting enabled, a DROP TABLE operation could cause a crash, due to a race condition that depended on the timing of pending I/O requests. (Bug #14594600, Bug #66718)

InnoDB: If an online DDL operation failed due to a duplicate key error, caused by DML changes being made concurrently to the table, the server could crash with an assertion error. (Bug #14591797)

InnoDB: A query against an InnoDB table with a FULLTEXT index could crash, if the AGAINST clause contained a character sequence that was encoded incorrectly for the character set of the table. (Bug #14588091)

InnoDB: If a FULLTEXT index was dropped from an InnoDB table, and the server crashed later for an unrelated reason, an additional error could occur while attempting to access nonexistent FULLTEXT data structures. (Bug #14586855)

InnoDB: The server could crash with a confusing message if it ran out of space for temporary files during index creation.

InnoDB: Assertion failure in thread thread_num in file mtr0mtr.cc line 306 
InnoDB: Failing assertion: mtr->state == 12231

(Bug #14586256)

InnoDB: An ALTER TABLE on an InnoDB table that dropped the primary key and then re-created it with columns in a different order could cause an error. The issue affected tables where the swapped columns referenced each other in a single-table foreign key relationship. The data dictionary could be left in an inconsistent state, where the table was listed in SHOW TABLES output but could not be queried or dropped. For example, if the table was declared with primary key columns (c1,c2) and a foreign key with c1 REFERENCES c2:

ALTER TABLE t2 DROP PRIMARY KEY, ADD PRIMARY KEY (c2, c1); 
ERROR 1030 (HY000): Got error 38 from storage engine 

(Bug #14548753)

InnoDB: During an online DDL operation, a ROLLBACK affecting the same table could cause an assertion error if the table formerly contained a FULLTEXT index. Some bookkeeping information related to FULLTEXT indexes for InnoDB tables is preserved even after such an index is dropped. (Bug #14503700)

InnoDB: If a table was defined with an index key length very close to the upper length limit of 3072, a query against that table could cause a serious error. (Bug #14500557, Bug #14537695)

InnoDB: Table names containing non-ASCII characters were displayed incorrectly when the MYSQL.INNODB_TABLE_STATS.TABLE_NAME column was queried. (Bug #14404879)

InnoDB: A race condition could cause a crash during an online CREATE INDEX statement for an InnoDB table. This bug only affected very small tables. It required a DML operation to be in progress for the table, affecting the primary key columns, at the same time the CREATE INDEX statement was issued. (Bug #14117641)

InnoDB: If a transaction was started with a consistent snapshot, then new indexes were added to the table while the transaction was in progress, a subsequent UPDATE statement could incorrectly encounter the error:

ER_TABLE_DEF_CHANGED: insufficient history for index

This issue could cause an assertion error in debug builds. (Bug #14036214)

InnoDB: The server could crash with an assertion error during operations on tables with ROW_FORMAT=COMPRESSED. (Bug #14001972)

InnoDB: In rare circumstances, during operations on an InnoDB table containing foreign keys, pages in the buffer pool could be evicted but not written to disk, leading to data inconsistency. (Bug #13688491)

InnoDB: In rare circumstances, MySQL could apply InnoDB undo records out of order during a ROLLBACK of an operation that modified a BLOB column. This issue could cause an assertion error in debug builds:

!bpage->file_page_was_freed 

(Bug #13249921)

InnoDB: In debug builds, a mismatch in the InnoDB PAGE_FREE list would cause an assertion. (Bug #12701488)

Partitioning: The server now skips pruning of tables (see Partition Pruning) that use a storage engine which handles its own partitioning internally. The server now also explicitly rejects attempts to use explicit partitioning for such tables. (Bug #14672885)

Partitioning: When used with a table having multiple columns in its primary key, but partitioned by KEY using a column that was not part of the primary key as the partitioning column, a query using an aggregate function and DISTINCT such as SELECT SUM(DISTINCT pk_column_1) FROM table WHERE pk_column_2 = constant was not handled correctly. (Bug #14495351)

Replication: When using a multi-threaded slave, if all worker threads were kept busy, it was possible for cleanup of an internal MTS circular buffer to fail, resulting in a full buffer and failure of the slave. (Bug #14710881)

Replication: Executing FLUSH LOGS in parallel with COMMIT could cause the server to hang. (Bug #14640486)

Replication: When invoked while gtid_mode was set to OFF, the SQL_THREAD_WAIT_AFTER_GTIDS() function waited indefinitely, unless a timeout was specified. In the latter case, the function could return incorrect values. Now, when gtid_mode is OFF, SQL_THREAD_WAIT_AFTER_GTIDS() always returns NULL, as expected. (Bug #14640065)

Replication: Partially-failed GRANT and REVOKE statements were not always handled the same way on the master and the slave. We now log an incident event whenever an error occurs, even if it is only a partial error, with a message stating that manual reconciliation is required. (Bug #14598585)

Replication: There existed a gap in time between the appending of the current GTID to the server's list of logged GTIDs and the commit of the transaction by the storage engine. On slow platforms, or when using profiling, this could cause SELECT SQL_THREAD_WAIT_AFTER_GTIDS(gtid) to return before the data actually reached the database.

Now the current GTID is appended to the logged GTIDs following the commit, which removes this gap and so eliminates a possible source of inconsistency. (Bug #14116526)

Replication: The error shown when a relay log file was missing from the relay log index file informed the user only that the log file was not found, but did not specify the exact reason. Now in such cases, the error message returned is Could not find target log file mentioned in relay log info in the index file 'index_file_name' during relay log initialization. (Bug #11758505)

Replication: Following an insert into a nontransactional table that failed due to insufficient disk space, the server did not properly clean up all pending events, leading to an assert or possibly to other errors. (Bug #11750014)

Replication: Backtick (`) characters were not always handled correctly in internally generated SQL statements, which could sometimes lead to errors on replication slaves or cause failure of restore operations from binary log files. (Bug #66550, Bug #14548159, Bug #29422, Bug #11746883)

A DELETE statement for an InnoDB table could write incorrect transaction metadata into a record, causing the server to halt with an error. To work around this issue, reduce the specified length of the primary key to less than 1K bytes. (Bug #14731482)

mysql_secure_installation could not change the password for an account that had password_expired='Y' in the mysql.user table row for that account. (Bug #14726722)

For an in-place ALTER TABLE operation on an InnoDB table that produced a duplicate-key error for NULL values, the error message displayed the column default value rather than NULL. (Bug #14723364)

Patches for materialized semi-joins caused failures of the query plan interface used by NDBCLUSTER. (Bug #14704659)

mysqladmin password did not work for accounts with an expired password. (The fix for this problem is limited to accounts with passwords that use native or “old” native hashing. It still does not handle accounts that use SHA-256 password hashing.)

As a consequence of this patch, the restricted mode of operation enforced by the server on operations permitted to clients with expired passwords now includes SET statements in addition to SET PASSWORD. This is useful if the account uses a password hashing format that requires old_passwords to be set to a value different from its default. (Bug #14698309)

Repeated execution of a query containing a subquery that used MAX() could result in increasing memory consumption. (Bug #14683676)

Queries that used a nested join with a subquery in the FROM clause and an ORDER BY ... DESC clause could return too few rows. (Bug #14678404)

With the optimizer tracing enabled, the INFORMATION_SCHEMA.OPTIMIZER_TRACE table can be queried to find tracing information about the last statements. However, for queries for which the results were retrieved from the query cache, this information was not available. (Bug #14665052)

There was a performance regression for queries using SELECT ... INTO user variables and a WHERE condition on one or more of the variables in the INTO list. (Bug #14664077)

References: This bug was introduced by Bug #12408412.

In debug builds, the server could crash because db_suicide() failed to handle SIGABRT signals. (Bug #14649493)

USE dbname could fail with Unknown database when dbname contained multiple backtick (`) characters. (Bug #14645196)

Outer joins could execute inefficiently and return incorrect results if joins were pushed down to the storage engine. (Bug #14644936)

A prepared statement that referenced views in an IN subquery could return different results for different executions. (Bug #14641759)

References: See also Bug #13773979.

Within a stored program, memory allocated to hold condition information was not released until program exit, leading to excessive memory use. (Bug #14640599)

Attempts to insert, update, delete from, or lock unknown Performance Schema tables failed with an ER_TABLEACCESS_DENIED_ERROR error rather than ER_NO_SUCH_TABLE. (Bug #14633008)

An incomplete result could be stored in the query cache when a query failed with an error (providing that the query cache was enabled, and was set to a nonzero size). This fix ensures that it is no longer possible for queries that finish with an error to be cached. (Bug #14621700)

References: This bug was introduced by Bug #40264.

The thread cache implementation worked in LIFO rather than FIFO fashion and could result in a thread being denied service (although this was a remote possibility). (Bug #14621627)

The server could crash when registering tables in the query cache for queries that selected from views. (Bug #14619935)

With semi-join and materialization optimizations enabled, a query that materialized a const table returned incorrect results when STRAIGHT_JOIN was added. (Bug #14609394)

Index condition pushdown in conjunction with descending index range scan could return incorrect results if there were multiple ranges in the range scan. (Bug #14604223)

EXPLAIN DELETE ... WHERE impossible_condition could function incorrectly when it was used in a stored routine. (Bug #14601802)

References: This bug was introduced by Bug #11752097.

Small values of max_sort_length could produce incorrect results for integer, decimal, floating-point, or temporal data types. Now max_sort_length is ignored for those data types. (Bug #14596888)

The configure.pl script that converts GNU configure options to CMake equivalents generated erroneous output for the --with-client-ldflags and --with-mysqld-ldflags options. It now ignores those options. (Bug #14593123)

A query with a subquery and ORDER BY and LIMIT clauses returned fewer rows than expected when executed using semi-join materialization. (Bug #14580874)

The server printed excessive Got error 159 when reading table messages to the error log when one transaction attempted to access a table that had been modified by another. (Bug #14579877)

The optimizer could choose an incorrect execution plan for updates to InnoDB tables based on indexes that use column prefixes. (Bug #14578060)

Materialization of a subquery in the FROM clause could return the wrong number of rows if the subquery included a LIMIT clause. (Bug #14576727)

In-source builds modified the source file sql/share/dictionary.txt. (Bug #14562699)

Improper memory cleanup could cause the server to exit. (Bug #14536113)

A query with a subquery in the JOIN ... ON clause with an outer reference to a field that was out of scope could cause the server to crash. (Bug #14498914)

On Windows, mysql_plugin could not find my_print_defaults. (Bug #14471052)

When used in GRANT statements, quoted user name or host name values containing leading or trailing spaces caused privileges to be assigned incorrectly until a FLUSH PRIVILEGES statement was issued.

Now, as a result of this fix, quoted name and host identifiers used in a GRANT statement are automatically trimmed of any leading and trailing spaces, before privileges are assigned. (Bug #14328259)

Granting or revoking the PROXY privilege caused the server to exit if the server was started with --skip-name-resolve. (Bug #14211140)

CREATE USER and DROP USER could fail to flush the privileges, requiring FLUSH PRIVILEGES to be used explicitly. (Bug #13864642)

On Mac OS X, the version_compile_machine system variable did not include the value 64 for server binaries compiled on a 64-bit system. (Bug #13859866)

Access to INFORMATION_SCHEMA tables through a view could leak memory. (Bug #13734987)

On Microsoft Windows with CMake 2.6, the build process would not stop if the create_initial_db step failed. (Bug #13713525)

The test in mysqld_safe for the presence of the --plugin_dir option and assignment of a default value to it were performed before the actual argument parsing took place. (Bug #13548161)

A cached query result was not empty at the end of statement execution as expected. This could occur when executing queries (with the query cache enabled and set to a nonzero size) where the result was not sent to the client such as those executed by the Event Scheduler, or when executing stored routines containing queries while the server was running in bootstrap mode. (Bug #11755580, Bug #14609893)

The number of connection errors from a given host as counted by the server was periodically reset, with the result that max_connect_errors was never reached and invalid hosts were never blocked from trying to connect. (Bug #11753779)

References: See also Bug #38247, Bug #43006, Bug #45584, Bug #45606.

The Range checked for each record optimization is now used for conditions with outer query references. (Bug #11750963)

Random number generation during client authentication consumed excessive CPU. (Bug #66567, Bug #14555434)

Metadata locking resulted in excessive contention in read-only workloads involving InnoDB tables and a low number of connections.

Now the set of metadata locks can be partitioned into separate hashes to permit connections accessing different objects to use different locking hashes and reduce contention. The new metadata_locks_hash_instances system variable can be used to specify the number of hashes. (Bug #66473, Bug #14569140)

On Windows, the Perl version of mysql_install_db created system tables in the mysql database that were not populated properly. (Bug #65584, Bug #14181049)

ST_Contains() and ST_Within() incorrectly reported that a polygon did not contain itself. ST_Equals() incorrectly returned 0 for polygons that differed only in shifted vertices. (Bug #64653, Bug #13864679)

ST_Difference() could incorrectly produce empty polygons in the result. (Bug #64649, Bug #13865773)

libmysqlclient did not use symbol versioning. Thanks to Nicholas Bamber for the patch. (Bug #64386, Bug #13788218)

The parser rejected legal queries that involved a UNION where the right hand side query term has a table in parenthese. (Bug #54382, Bug #11761854)

For some queries involving ORDER BY, the optimizer chose the wrong index for accessing the table. (Bug #45969, Bug #11754370, Bug #14338686)

In debug builds, vio_read() printed errno rather than socket_error to the debug trace. (Bug #28775, Bug #11746795)