MySQL Community Edition is a freely downloadable version of the world's most popular open source database that is supported by an active community of open source developers and enthusiasts.
MySQL delivers enterprise features, including:
- Partitioning to improve performance and management of very large database environments
- Row-based/Hybrid Replication for improved replication security
- Event Scheduler to create and schedule jobs that perform various database tasks
- XPath Support
- Dynamic General/Slow Query Log
- Performance/Load Testing Utility (mysqlslap)
- Improved! Full Text Search (faster, new dev templates)
- Improved! Archive engine (better compression, more features)
- Improved! User session and problem SQL identification
- Improved! MySQL embedded library (libmysqld)
- Additional INFORMATION_SCHEMA objects
- Faster data import operations (parallel file load)
- ACID Transactions to build reliable and secure business critical applications
- Stored Procedures to improve developer productivity
- Triggers to enforce complex business rules at the database level
- Views to ensure sensitive information is not compromised
- Information Schema to provide easy access to metadata
- Pluggable Storage Engine Architecture for maximum flexibility
- Archive Storage Engine for historical and audit data
# Functionality Added or Changed
* Incompatible Change: The AES_ENCRYPT() and AES_DECRYPT() functions now permit control of the block encryption mode and take an optional initialization vector argument:
- The new block_encryption_mode system variable controls the mode for block-based encryption algorithms. Its default value is aes-128-ecb, which signifies encryption using a key length of 128 bits and ECB mode.
- An optional init_vector argument provides an initialization vector for encryption modes that require it:
- A random string of bytes to use for the initialization vector can be produced by calling the new RANDOM_BYTES() function.
* Incompatible Change: The deprecated ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE SQL modes now do nothing. Instead, their previous effects are included in the effects of strict SQL mode (STRICT_ALL_TABLES or STRICT_TRANS_TABLES). In other words, strict mode now means the same thing as the previous meaning of strict mode plus the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes. This change reduces the number of SQL modes with an effect dependent on strict mode and makes them part of strict mode itself.
* InnoDB: MySQL now supports rebuilding regular and partitioned InnoDB tables using online DDL (ALGORITHM=INPLACE) for the following operations:
- OPTIMIZE TABLE
- ALTER TABLE ... FORCE
- ALTER TABLE ... ENGINE=INNODB (when run on an InnoDB table)
* On Solaris, mysql_config --libs now includes -R/path/to/library so that libraries can be found at runtime.
* mysql_install_db provides a more informative diagnostic message when required Perl modules are missing.
* The IGNORE clause for ALTER TABLE is now deprecated and will be removed in a future version of MySQL. ALTER IGNORE TABLE causes problems for replication, prevents online ALTER TABLE for unique index creation, and causes problems with foreign keys (rows removed in the parent table).
# Bugs Fixed
* Incompatible Change: Old clients (older than MySQL 5.5.7) failed to parse authentication data correctly if the server was started with the --default-authentication-plugin=sha256_password option.
* Important Change; InnoDB; Partitioning: The FLUSH TABLES statement's FOR EXPORT option is now supported for partitioned InnoDB tables.
* InnoDB: Running a SELECT on a partitioned table caused a memory access violation in memcpy().
* InnoDB: An invalid memmove in fts_query_fetch_document would cause a serious error.
* InnoDB: For full-text queries, a failure to check that num_token is less than max_proximity_item could result in an assertion.
* InnoDB: innodb_ft_result_cache_limit now has a hardcoded maximum value of 4294967295 bytes or (2**32 -1). The maximum value was previously defined as the maximum value of ulong.
* InnoDB: InnoDB would fail to restore a corrupt first page of a system tablespace data file from the doublewrite buffer, resulting in a startup failure.
* InnoDB: An UPDATE resulted in a memory access error in lock_rec_other_trx_holds_expl. The transaction list (trx_sys->rw_trx_list) was traversed without acquiring the transaction subsystem mutex (trx_sys->mutex).
* InnoDB: A regression introduced would result in a performance degradation when a compressed table does not fit into memory.
* InnoDB: The maximum value for innodb_thread_sleep_delay is now 1000000 microseconds. The previous maximum value (4294967295 microseconds on 32-bit and 18446744073709551615 microseconds on 64-bit) was unnecessarily large. Because the maximum value of innodb_thread_sleep_delay is limited by the value set for innodb_adaptive_max_sleep_delay (when set to a non-zero value), the maximum value for innodb_thread_sleep_delay is now the same as the maximum value for innodb_adaptive_max_sleep_delay.
* InnoDB: A full-text tokenizer thread would terminate with an incorrect error message.
* InnoDB: Attempting to uninstall the InnoDB memcached plugin while the InnoDB memcached plugin is still initializing would kill the InnoDB memcached daemon thread. Uninstall should wait until initialization is complete.
* InnoDB: In debug builds, creating a unique index on a binary column, with input data containing duplicate keys, would cause an assertion.
* InnoDB: The srv_monitor_thread would crash in the lock_print_info_summary() function due to a race condition between the srv_monitor_thread and purge coordinator thread.
* InnoDB: Attempting to add an invalid foreign key when foreign key checking is disabled (foreign_key_checks=0) would cause a serious error.
* InnoDB: For debug builds, the table rebuilding variant of online ALTER TABLE, when run on tables with BLOB columns, would cause an assertion in the row_log_table_apply_update function. For normal builds, a DB_PRODUCTION error would be returned.
* InnoDB: When creating a table there are a minimum of three separate inserts on the mysql.innodb_index_stats table. To improve CREATE TABLE performance, there is now a single COMMIT operation instead of one for each insert.
* InnoDB: The server would halt with an assertion in lock_rec_has_to_wait_in_queue(lock) due to a locking-related issue and a transaction being prematurely removed from trx_sys->rw_trx_set.
* InnoDB: Server shutdown would result in a hang with the following message written to the error log: “[NOTE] InnoDB: Waiting for purge thread to be suspended.”
* InnoDB: InnoDB would fail to start when innodb_data_file_path specified the data file size in kilobytes by appending K to the size value.
* InnoDB: An insert buffer merge would cause an assertion error due to incorrectly handled ownership information for externally stored BLOBs.
* InnoDB: Assertion failure in thread thread_num in file ibuf0ibuf.cc line 4080
* InnoDB: Failing assertion: rec_get_deleted_flag(rec, page_is_comp(page))
* InnoDB: Decreasing the auto_increment_increment value would have no affect on the next auto-increment value.
* Partitioning: When the index_merge_intersection flag (enabled by default) or the index_merge_union flag was enabled by the setting of the optimizer_switch system variable, queries returned incorrect results when executed against partitoned tables that used the MyISAM storage engine, as well as partitioned InnoDB tables that lacked a primary key.
* Replication: The MASTER_SSL_CRL and MASTER_SSL_CRLPATH options are not available when using yaSSL; MySQL Replication now sets these to NULL automatically whenever yaSSL is enabled.
* Replication: Setting --slave-parallel-workers to 1 or greater and starting the slave caused the slave SQL thread to use but not release memory until the slave was restarted with STOP SLAVE and START SLAVE.
* Replication: When a slave was configured with replication filters and --log-warnings=2, every statement which was filtered caused an entry to be written in the error log. For busy servers which generated many statements to be filtered, the result was that the error log could quickly grow to many gigabytes in size. Now a throttle is used for such errors, so that an error message is printed only once in a given interval, saying that this particular error occurred a specific number of times during that interval.
* Replication: SHOW SLAVE STATUS used incorrect values when reporting MASTER_SSL_CRL and MASTER_SSL_CRLPATH.
* Replication: Binary log events could be sent to slaves before they were flushed to disk on the master, even when sync_binlog was set to 1. This could lead to either of those of the following two issues when the master was restarted following a crash of the operating system:
- Replication cannot continue because one or more slaves are requesting replicate events that do not exist on the master.
- Data exists on one or more slaves, but not on the master.
* Replication: When running the slave with --slave-parallel-workers at 1 or greater, setting --slave-skip-errors=all caused the error log to be filled with with instances of the warning Slave SQL: Could not execute Query event. Detailed error: ;, Error_code: 0.
* Replication: A number of possible state messages used as values for the PROCESSLIST_STATE column of the Performance Schema threads table were longer than the width of the column (64 characters).
* Replication: The server did not handle correctly the insertion of a row larger than 4 GB when using row-based replication.
* Replication: When using row-based replication, an additional auto-increment column on the slave version of a table was not updated correctly; a zero was inserted instead.
* Replication: Statements involving the Performance Schema tables should not be written to the binary log, because the content of these tables is applicable only to a given MySQL Server instance, and may differ greatly between different servers in a replication topology. The database administrator should be able to configure (INSERT, UPDATE, or DELETE) or flush (TRUNCATE TABLE) performance schema tables on a single server without affecting others. However, when replicating from a MySQL 5.5 master to a MySQL 5.5 or later slave, warnings about unsafe statements updating Performance Schema tables were elevated to errors. For MySQL 5.6 and later slaves, this prevented the simultaneous use of performance_schema and GTIDs
* Replication: Modifying large amounts of data within a transaction can cause the creation of temporary files. Such files are created when the size of the data modified exceeds the size of the binary log cache (max_binlog_cache_size). Previously, such files persisted until the client connection was closed, which could allow them to grow until they exhausted all available disk space in tmpdir. To prevent this from occurring, the size of a temporary file created in this way in a given transaction is now reset to 0 when the transaction is committed or rolled back.
* Replication: The server checks to determine whether semisynchronous replication has been enabled without a lock, and if this is the case, it takes the lock and checks again. If semisynchronous replication was disabled after the first but prior to the second one, this could cause the server to fail.
* Replication: Semisynchronous replication became very slow if there were many dump threads (such as from mysqlbinlog or slave I/O connections) working at the same time. It was also found that semisynchronous master plugin functions were called even when the dump connections did not support semisynchronous replication, which led to locking of the plugin lock as well as wasting time on necessary code.
* After this fix, non-semisynchronous dump threads no longer call semisynchronous master functions to observe binary events.
* mysql_install_db could hang while reading /dev/random to generate a random root password.
* Compilation failed if MySQL was configured with CFLAGS set to include a -Werror option with an argument.
* A shared libmysqld embedded server library was not built on Linux.
* While printing the server version, the mysql client did not check for buffer overflow in a string variable.
* Building MySQL from source on Windows using Visual Studio 2008 would fail with an identifier not found error due to a regression
* On Microsoft Windows, the rw-lock backup implementation for the my_atomic_* functions was always used. Now, the native Microsoft Windows implementation is used, where available.
* When tables are reopened from the table cache and the current thread is not instrumented for the Performance Schema, a table handle was unnecessarily instrumented.
* The audit log plugin could cause a server exit during log file rotation operations when there were many operations happening for multiple connections.
* The SUM_SORT_MERGE_PASSES column value in the Performance Schema events_statements_summary_by_digest table was calculated incorrectly.
* If the Performance Schema events_statements_summary_by_digest table was full when a statement with a new digest was found, the Performance_schema_digest_lost status variable was not incremented.
* The optimizer could push down a condition when the index did not have the key part present in the condition.
* Contraction information in a collation could be mishandled, resulting in incorrect decisions about whether a character is part of a contraction, and miscalculation of contraction weights.
* DROP TRIGGER succeeded even with the read_only system variable enabled.
* If used to process a prepared CALL statement for a stored procedure with OUT or INOUT parameters, mysql_stmt_store_result() did not properly set the flags required to retrieve all the result sets.
* When run by root, mysqld --help --verbose exited with a nonzero error code after displaying the help message.
* MySQL client programs from a Community Edition distribution could not connect using SSL to a MySQL server from an Enterprise Edition. This was due to a difference in certificate handling by yaSSL and OpenSSL (used for Community and Enterprise, respectively). OpenSSL expected a blank certificate to be sent when not all of the --ssl-ca, --ssl-cert, and --ssl-key options were specified, and yaSSL did not do so. To resolve this, yaSSL has been modified to send a blank certificate when an option is missing.
* The mysqladmin, mysqlbinlog, mysqlcheck, mysqldump, mysqlimport, mysqlslap, and mysqlshow programs now support a --secure-auth option that prevents sending passwords to the server in old (pre-4.1) format. This option is enabled by default; use --skip-secure-auth to disable it.
* A deadlock error occurring during subquery execution could cause an assertion to be raised.
* The Performance Schema stage/sql/Waiting to get readlock instrument is no longer used and has been removed.
* A query that creates a temporary table to find distinct values and has a constant value in the projected list could produce incorrect results.
* Messages written by the server to the error log for LDML collation definition problems were missing the collation name.
* mysqlcheck did not correctly handle table names containing dots.
* Aggregating the results of a subquery in the FROM clause could produce incorrect results.
* For system variables that take a string value, SET statements permitted an unquoted value, but values that contained dots were parsed incorrectly and only part of the value was assigned. For example, SET GLOBAL slow_query_log_file = my_slow.log assigned the value my_slow. Now such values must be quoted or an error occurs.
* A temporal literal string without delimiters and more than 14 digits was validated as a TIMESTAMP/DATETIME value with a two-digit precision fractional seconds part. But fractional seconds should always be separated from other parts of a time by a decimal point.
* The msql2mysql, mysql_convert_table_format, mysql_find_rows, mysql_fix_extensions, mysql_setpermission, and mysqlaccess utilities are now deprecated and will be removed in MySQL 5.7.