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
* InnoDB: The innodb_print_all_deadlocks configuration option from MySQL 5.6 was backported to MySQL 5.5. This option records each deadlock condition in the MySQL error log, allowing easier troubleshooting if frequent deadlocks point to application coding issues.
* In RPM packages built for Unbreakable Linux Network, libmysqld.so now has a version number.
# Bugs Fixed
* InnoDB; Performance: Some data structures related to undo logging could be initialized unnecessarily during a query, although they were only needed under specific conditions.
* InnoDB; Performance: Optimized read operations for compressed tables by skipping redundant tests. The check for whether any related changes needed to be merged from the insert buffer was being called more often than necessary.
* InnoDB; Performance: Immediately after a table was created, queries against it would not use loose index scans. The issue went away following an ALTER TABLE on the table. The fix improves the accuracy of the index statistics gathered when the table is first created, and prevents the query plan from being changed by the ALTER TABLE statement.
* InnoDB; Partitioning: Previously, when attempting to optimize one or more partitions of a partitioned table that used a storage engine that does not support partition-level OPTIMIZE, such as InnoDB, MySQL reported Table does not support optimize, doing recreate + analyze instead, then re-created the entire table, but did not actually analyze it. Now in such cases, the warning message is, Table does not support optimize on partitions. All partitions will be rebuilt and analyzed. In addition, the entire table is analyzed after first being rebuilt.
* InnoDB: On systems that cannot handle unaligned memory access, depending on the stack frame alignment, a SIGBUS error could occur during startup. This issue was observed on Solaris 64-bit systems.
* InnoDB: The status variable Innodb_buffer_pool_read_ahead_evicted could show an inaccurate value, higher than expected, because some pages in the buffer pool were incorrectly considered as being brought in by read-ahead requests.
* InnoDB: Creating an index on a CHAR column could fail for a table with a character set with varying length, such as UTF-8, if the table was created with the ROW_FORMAT=REDUNDANT clause.
* InnoDB: The server could halt with an assertion error while creating an index: InnoDB: Assertion failure in thread thread_num in file row0merge.cc line 465 This issue affected tables with a combination of ROW_FORMAT=REDUNDANT off-page columns, and an index on a column prefix.
* InnoDB: If the server crashed at a precise moment during an ALTER TABLE operation that rebuilt the clustered index for an InnoDB table, the original table could be inaccessible afterward. An example of such an operation is ALTER TABLE ... ADD PRIMARY KEY The fix preserves the original table if the server halts during this operation. You might still need to rename the .ibd file manually to restore the original table contents: in MySQL 5.6 and higher, rename from #sql-ib$new_table_id.ibd to table_name.ibd within the database directory; prior to MySQL 5.6, the temporary file to rename is table_name#1 or #2.
* InnoDB: An error at the filesystem level, such as too many open files, could cause an unhandled error during an ALTER TABLE operation. The error could be accompanied by Valgrind warnings, and by this assertion message: Assertion `! is_set()' failed. mysqld got signal 6 ;
* InnoDB: A RENAME TABLE statement could stall for several minutes before timing out. This issue could occurred for a table using compression, with change buffering enabled.
* InnoDB: During shutdown, with the innodb_purge_threads configuration option set greater than 1, the server could halt prematurely with this error: mysqld got signal 11 A workaround was to increase innodb_log_file_size and set innodb_purge_threads=1. The fix was backported to MySQL 5.5 and 5.1, although those versions do not have the innodb_purge_threads configuration option so the error was unlikely to occur.
* InnoDB: If the value of innodb_force_recovery was less than 6, opening a corrupted table might loop forever if a corrupted page was read when calculating statistics for the table. Information about the corrupted page was written repeatedly to the error log, possibly causing a disk space issue. The fix causes the server to halt after a fixed number of failed attempts to read the page. To troubleshoot such a corruption issue, set innodb_force_recovery=6 and restart.
* InnoDB: The value of the innodb_version variable was not updated consistently for all server releases for the InnoDB Plugin in MySQL 5.1, and the integrated InnoDB component in MySQL 5.5, 5.6, and higher. Since InnoDB and MySQL Server development cycles are fully integrated and synchronized, now the value returned by the innodb_version variable is the same as for the version variable.
* Partitioning: Concurrent ALTER TABLE ... REBUILD PARTITION operations could interfere with one another, even when not running against the same table, because they both used global memory for storage. Now each partition rebuild operation stores intermediate data in memory that is local to that process.
* Partitioning: Inserting any number of rows into an ARCHIVE table that used more than 1000 partitions and then attempting to drop the table caused the MySQL Server to fail.
* Replication: After dropping a column from the slave's version of a table, then altering the same column of this table on the master (so that a type conversion would have been required had the column not been droppped on the slave), inserts into this table caused replication to fail.
* Replication: When a binary log is replayed on a server (for example, by executing a command like mysqlbinlog binlog.000001 | mysql), it sets a pseudo-slave mode on the client connection used, so that the server can read binlog and apply binary log events correctly. However, the pseudo-slave mode was not disabled after the binary log dump was read, which caused unexpected filtering rules to be applied to SQL statements subsequently executed on the same connection.
* Replication: When using statement-based replication, and where the master and the slave used table schemas having different AUTO_INCREMENT columns, inserts generating AUTO_INCREMENT values logged for a given table on the master could be applied to the wrong table on the slave.
* Replication: Repeated execution of CHANGE MASTER TO statements using invalid MASTER_LOG_POS values could lead to errors and possibly a crash on the slave. Now in such cases, the statement fails with a clear error message.
* Replication: If the disk becomes full while writing to the binary log, the server hangs until space is freed up manually. It was possible after this was done for the MySQL server to fail, due to an internal status value being set when not needed. Now in such cases, rather than trying to set this status, a warning is written in the error log instead.
* Microsoft Windows: Dynamic file names (with colons) are no longer allowed. Static file names using the Alternate Data Stream (ADS) NTFS functionality of Microsoft Windows may continue to be used.
* Joins of exactly 32 tables and containing a HAVING clause returned an empty result.
* A buffer-handling problem in yaSSL was fixed.
* A mysys library string-formatting routine could mishandle width specifiers.
* In certain cases, UpdateXML() could return NULL incorrectly.
* Metadata locking and table definition cache routines did not always check length of names passed to them.
* XA START had a race condition that could cause a server crash.
* Enabling the query cache during high client contention could cause the server to exit.
* 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.
* The server sometimes failed to respect MAX_CONNECTIONS_PER_HOUR limits on user connections.
* Output generated with mysqldump --routines could produce syntax errors when reloaded.
* With the thread pool plugin installed, a workload consisting of concurrent KILL statements and ping queries caused the server to exit.
* CHECK TABLE and REPAIR TABLE could crash if a MyISAM table had a corrupt key (.MYI) file. Now the server produces an error.
* Passing an unknown time zone specification to CONVERT_TZ() resulted in a memory leak.
* For dumps of the mysql database, mysqldump skipped the event table unless the --events option was given. To skip this table if that is desired, use the --ignore-table option instead
* For MEMORY tables with HASH indexes, DELETE sometimes failed to delete all applicable rows.
* The mysql client could mishandle the delimiter command if it occurred on a line during which mysql was looking for the end of a quoted string.
* mysqld_safe used the nonportable -e test construct.
* Configuring the server with performance_schema_events_waits_history_size=0 and performance_schema_events_waits_history_long_size=0 could cause a Performance Schema segmentation fault.
* DECIMAL multiplication operations could produce significant inaccuracy.
* For subqueries executing using a filesort, the optimizer could produce an incorrect result containing wrong rows.
* UNION type conversion could incorrectly turn unsigned values into signed values.
* During the startup process, mysqld could incorrectly remove the PID file of an already running mysqld.