1.4 What Is New in MySQL 5.6

This section summarizes what has been added to, deprecated in, and removed from MySQL 5.6.

• Features Added in MySQL 5.6

• Features Deprecated in MySQL 5.6

• Features Removed in MySQL 5.6

Features Added in MySQL 5.6

The following features have been added to MySQL 5.6:

• Security improvements.  These security improvements were made:

  • MySQL now provides a method for storing authentication credentials encrypted in an option file named .mylogin.cnf. To create the file, use the mysql_config_editor utility. The file can be read later by MySQL client programs to obtain authentication credentials for connecting to a MySQL server. mysql_config_editor writes the .mylogin.cnf file using encryption so the credentials are not stored as clear text, and its contents when decrypted by client programs are used only in memory. In this way, passwords can be stored in a file in non-cleartext format and used later without ever needing to be exposed on the command line or in an environment variable. For more information, see Section 4.6.6, “mysql_config_editor — MySQL Configuration Utility”.

  • MySQL now supports stronger encryption for user account passwords, available through an authentication plugin named sha256_password that implements SHA-256 password hashing. This plugin is built in, so it is always available and need not be loaded explicitly. For more information, including instructions for creating accounts that use SHA-256 passwords, see Section 6.4.1.4, “SHA-256 Pluggable Authentication”.

  • The mysql.user system table now has a password_expired column. Its default value is 'N', but can be set to 'Y' with the new ALTER USER statement. After an account's password has been expired, all operations performed in subsequent connections to the server using the account result in an error until the user issues a SET PASSWORD statement to establish a new account password. For more information, see Section 13.7.1.1, “ALTER USER Syntax”, and Section 6.2.10, “Server Handling of Expired Passwords”.

  • MySQL now has provision for checking password security:

    • In statements that assign a password supplied as a cleartext value, the value is checked against the current password policy and rejected if it is weak (the statement returns an ER_NOT_VALID_PASSWORD error). This affects the CREATE USER, GRANT, and SET PASSWORD statements. Passwords given as arguments to the PASSWORD() and OLD_PASSWORD() functions are checked as well.

    • The strength of potential passwords can be assessed using the new VALIDATE_PASSWORD_STRENGTH() SQL function, which takes a password argument and returns an integer from 0 (weak) to 100 (strong).

    Both capabilities are implemented by the validate_password plugin. For more information, see Section 6.4.3, “The Password Validation Plugin”.

  • mysql_upgrade now produces a warning if it finds user accounts with passwords hashed with the older pre-4.1 hashing method. Such accounts should be updated to use more secure password hashing. See Section 6.1.2.4, “Password Hashing in MySQL”

  • 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 assign a random password to the MySQL root accounts, set the “password expired” flag for those accounts, and remove the anonymous-user MySQL accounts. For additional details, see Section 4.4.3, “mysql_install_db — Initialize MySQL Data Directory”.

  • Logging has been modified so that passwords do not appear in plain text in statements written to the general query log, slow query log, and binary log. See Section 6.1.2.3, “Passwords and Logging”.

    The mysql client no longer logs to its history file statements that refer to passwords. See Section 4.5.1.3, “mysql Client Logging”.

  • START SLAVE syntax has been modified to permit connection parameters to be specified for connecting to the master. This provides an alternative to storing the password in the master.info file. See Section 13.4.2.5, “START SLAVE Syntax”.

  • MySQL now sets the access control granted to clients on the named pipe to the minimum necessary for successful communication on Windows. Newer MySQL client software can open named pipe connections without any additional configuration. If older client software cannot be upgraded immediately, the new named_pipe_full_access_group system variable can be used to give a Windows group the necessary permissions to open a named pipe connection. Membership in the full-access group should be restricted and temporary.

• MySQL Enterprise.  The format of the file generated by the audit log plugin was changed for better compatibility with Oracle Audit Vault. See Section 6.4.4, “MySQL Enterprise Audit”, and Section 6.4.4.3, “Audit Log File Formats”.

  MySQL Enterprise Edition now includes a set of encryption functions based on the OpenSSL library that expose OpenSSL capabilities at the SQL level. These functions enable Enterprise applications to perform the following operations:

  • Implement added data protection using public-key asymmetric cryptography

  • Create public and private keys and digital signatures

  • Perform asymmetric encryption and decryption

  • Use cryptographic hashing for digital signing and data verification and validation

  For more information, see Section 12.18, “MySQL Enterprise Encryption Functions”.

  The audit log plugin included in MySQL Enterprise Edition now has the capability of filtering audited events based on user account and event status. Several new system variables provide DBAs with filtering control. In addition, audit log plugin reporting capability has been improved by the addition of several status variables. For more information, see Section 6.4.4.4, “Audit Log Logging Control”, and Audit Log Plugin Status Variables.

  MySQL Enterprise Edition now includes MySQL Enterprise Firewall, an application-level firewall that enables database administrators to permit or deny SQL statement execution based on matching against whitelists of accepted statement patterns. This helps harden MySQL Server against attacks such as SQL injection or attempts to exploit applications by using them outside of their legitimate query workload characteristics. For more information, see Section 6.4.5, “MySQL Enterprise Firewall”.

• Changes to server defaults.  Beginning with MySQL 5.6.6, several MySQL Server parameter defaults differ from the defaults in previous releases. 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. For more information, see Section 5.1.2.1, “Changes to Server Defaults”.

• InnoDB enhancements.  These InnoDB enhancements were added:

  • You can create FULLTEXT indexes on InnoDB tables, and query them using the MATCH() ... AGAINST syntax. This feature includes a new proximity search operator (@) and several new configuration options and INFORMATION_SCHEMA tables: See Section 14.6.2.3, “InnoDB FULLTEXT Indexes” for more information.

  • Several ALTER TABLE operations can be performed without copying the table, without blocking inserts, updates, and deletes to the table, or both. These enhancements are known collectively as online DDL. See Section 14.13, “InnoDB and Online DDL” for details.

  • InnoDB now supports the DATA DIRECTORY='directory' clause of the CREATE TABLE statement, which allows you to create InnoDB file-per-table tablespaces (.ibd files) in a location outside the MySQL data directory. This enhancement provides the flexibility to create file-per-table tablespaces in locations that better suit your server environment. For example, you could place busy tables on an SSD device, or large tables on a high-capacity HDD device.

    For additional information, see Section 14.6.3.4, “Creating a Tablespace Outside of the Data Directory”.

  • InnoDB now supports the notion of “transportable tablespaces”, allowing file-per-table tablespaces (.ibd files) to be exported from a running MySQL instance and imported into another running instance without inconsistencies or mismatches caused by buffered data, in-progress transactions, and internal bookkeeping details such as the space ID and LSN.

    The FOR EXPORT clause of the FLUSH TABLE command writes any unsaved changes from InnoDB memory buffers to the .ibd file. After copying the .ibd file and a separate metadata file to the other server, the DISCARD TABLESPACE and IMPORT TABLESPACE clauses of the ALTER TABLE statement are used to bring the table data into a different MySQL instance.

    This enhancement provides the flexibility to move file-per-table tablespaces around to better suit your server environment. For example, you could move busy tables to an SSD device, or move large tables to a high-capacity HDD device. For more information, see Section 14.6.3.5, “Copying Tablespaces to Another Instance”.

  • You can now set the InnoDB page size for uncompressed tables to 8KB or 4KB, as an alternative to the default 16KB. This setting is controlled by the innodb_page_size configuration option. You specify the size when creating the MySQL instance. All InnoDB tablespaces within an instance share the same page size. Smaller page sizes can help to avoid redundant or inefficient I/O for certain combinations of workload and storage devices, particularly SSD devices with small block sizes.

  • Improvements to the algorithms for adaptive flushing make I/O operations more efficient and consistent under a variety of workloads. The new algorithm and default configuration values are expected to improve performance and concurrency for most users. Advanced users can fine-tune their I/O responsiveness through several configuration options. See Section 14.8.3.4, “Configuring Buffer Pool Flushing” for details.

  • You can code MySQL applications that access InnoDB tables through a NoSQL-style API. This feature uses the popular memcached daemon to relay requests such as ADD, SET, and GET for key-value pairs. These simple operations to store and retrieve data avoid the SQL overhead such as parsing and constructing a query execution plan. You can access the same data through the NoSQL API and SQL. For example, you might use the NoSQL API for fast updates and lookups, and SQL for complex queries and compatibility with existing applications. See Section 14.20, “InnoDB memcached Plugin” for details.

  • Optimizer statistics for InnoDB tables are gathered at more predictable intervals and can persist across server restarts, for improved plan stability. You can also control the amount of sampling done for InnoDB indexes, to make the optimizer statistics more accurate and improve the query execution plan. See Section 14.8.11.1, “Configuring Persistent Optimizer Statistics Parameters” for details.

  • New optimizations apply to read-only transactions, improving performance and concurrency for ad-hoc queries and report-generating applications. These optimizations are applied automatically when practical, or you can specify START TRANSACTION READ ONLY to ensure the transaction is read-only. See Section 8.5.3, “Optimizing InnoDB Read-Only Transactions” for details.

  • You can move the InnoDB undo log out of the system tablespace into one or more separate tablespaces. The I/O patterns for the undo log make these new tablespaces good candidates to move to SSD storage, while keeping the system tablespace on hard disk storage. For details, see Section 14.6.3.3, “Undo Tablespaces”.

  • You can improve the efficiency of the InnoDB checksum feature by specifying the configuration option innodb_checksum_algorithm=crc32, which turns on a faster checksum algorithm. This option replaces the innodb_checksums option. Data written using the old checksum algorithm (option value innodb) is fully upward-compatible; tablespaces modified using the new checksum algorithm (option value crc32) cannot be downgraded to an earlier version of MySQL that does not support the innodb_checksum_algorithm option.

  • The InnoDB redo log files now have a maximum combined size of 512GB, increased from 4GB. You can specify the larger values through the innodb_log_file_size option. The startup behavior now automatically handles the situation where the size of the existing redo log files does not match the size specified by innodb_log_file_size and innodb_log_files_in_group.

  • The --innodb-read-only option lets you run a MySQL server in read-only mode. You can access InnoDB tables on read-only media such as a DVD or CD, or set up a data warehouse with multiple instances all sharing the same data directory. See Section 14.8.2, “Configuring InnoDB for Read-Only Operation” for usage details.

  • A new configuration option, innodb_compression_level, allows you to select a compression level for InnoDB compressed tables, from the familiar range of 0-9 used by zlib. You can also control whether compressed pages in the buffer pool are stored in the redo log when an update operation causes pages to be compressed again. This behavior is controlled by the innodb_log_compressed_pages configuration option.

  • Data blocks in an InnoDB compressed table contain a certain amount of empty space (padding) to allow DML operations to modify the row data without re-compressing the new values. Too much padding can increase the chance of a compression failure, requiring a page split, when the data does need to be re-compressed after extensive changes. The amount of padding can now be adjusted dynamically, so that DBAs can reduce the rate of compression failures without re-creating the entire table with new parameters, or re-creating the entire instance with a different page size. The associated new configuration options are innodb_compression_failure_threshold_pct, innodb_compression_pad_pct_max.

  • Several new InnoDB-related INFORMATION_SCHEMA tables provide information about the InnoDB buffer pool, metadata about tables, indexes, and foreign keys from the InnoDB data dictionary, and low-level information about performance metrics that complements the information from the Performance Schema tables.

  • To ease the memory load on systems with huge numbers of tables, InnoDB now frees up the memory associated with an opened table using an LRU algorithm to select tables that have gone the longest without being accessed. To reserve more memory to hold metadata for open InnoDB tables, increase the value of the table_definition_cache configuration option. InnoDB treats this value as a “soft limit” for the number of open table instances in the InnoDB data dictionary cache. For additional information, refer to the table_definition_cache documentation.

  • InnoDB has several internal performance enhancements, including reducing contention by splitting the kernel mutex, moving flushing operations from the main thread to a separate thread, enabling multiple purge threads, and reducing contention for the buffer pool on large-memory systems.

  • InnoDB uses a new, faster algorithm to detect deadlocks. Information about all InnoDB deadlocks can be written to the MySQL server error log, to help diagnose application issues.

  • To avoid a lengthy warmup period after restarting the server, particularly for instances with large InnoDB buffer pools, you can reload pages into the buffer pool immediately after a restart. MySQL can dump a compact data file at shutdown, then consult that data file to find the pages to reload on the next restart. You can also manually dump or reload the buffer pool at any time, for example during benchmarking or after complex report-generation queries. See Section 14.8.3.5, “Saving and Restoring the Buffer Pool State” for details.

  • As of MySQL 5.6.16, innochecksum provides support for files greater than 2GB in size. Previously, innochecksum only supported files up to 2GB in size.

  • As of MySQL 5.6.16, new global configuration parameters, innodb_status_output and innodb_status_output_locks, allow you to dynamically enable and disable the standard InnoDB Monitor and InnoDB Lock Monitor for periodic output. Enabling and disabling monitors for periodic output by creating and dropping specially named tables is deprecated and may be removed in a future release. For additional information, see Section 14.17, “InnoDB Monitors”.

  • As of MySQL 5.6.17, Online DDL support is extended to the following operations for regular and partitioned InnoDB tables:

    • OPTIMIZE TABLE

    • ALTER TABLE ... FORCE

    • ALTER TABLE ... ENGINE=INNODB (when run on an InnoDB table)

      Online DDL support reduces table rebuild time and permits concurrent DML. See Section 14.13, “InnoDB and Online DDL”.

  • As of MySQL 5.6.42, the zlib library version bundled with MySQL was raised from version 1.2.3 to version 1.2.11. MySQL implements compression with the help of the zlib library.

    If you use InnoDB compressed tables, see Section 2.11.3, “Changes in MySQL 5.6” for related upgrade implications.

• Partitioning.  These table-partitioning enhancements were added:

  • The maximum number of partitions is increased to 8192. This number includes all partitions and all subpartitions of the table.

  • It is now possible to exchange a partition of a partitioned table or a subpartition of a subpartitioned table with a nonpartitioned table that otherwise has the same structure using the ALTER TABLE ... EXCHANGE PARTITION statement. This can be used, for example, to import and export partitions. For more information and examples, see Section 19.3.3, “Exchanging Partitions and Subpartitions with Tables”.

  • Explicit selection of one or more partitions or subpartitions is now supported for queries, as well as for many data modification statements, that act on partitioned tables. For example, assume a table t with some integer column c has 4 partitions named p0, p1, p2, and p3. Then the query SELECT * FROM t PARTITION (p0, p1) WHERE c < 5 returns only those rows from partitions p0 and p1 for which c is less than 5.

    The following statements support explicit partition selection:

    • SELECT

    • DELETE

    • INSERT

    • REPLACE

    • UPDATE

    • LOAD DATA.

    • LOAD XML.

    For syntax, see the descriptions of the individual statements. For additional information and examples, see Section 19.5, “Partition Selection”.

  • Partition lock pruning greatly improves performance of many DML and DDL statements acting on tables with many partitions by helping to eliminate locks on partitions that are not affected by these statements. Such statements include many SELECT, SELECT ... PARTITION, UPDATE, REPLACE, INSERT, as well as many other statements. For more information, including a complete listing of the statements whose performance has thus been improved, see Section 19.6.4, “Partitioning and Locking”.

• Performance Schema.  The Performance Schema includes several new features:

  • Instrumentation for table input and output. Instrumented operations include row-level accesses to persistent base tables or temporary tables. Operations that affect rows are fetch, insert, update, and delete.

  • Event filtering by table, based on schema and/or table names.

  • Event filtering by thread. More information is collected for threads.

  • Summary tables for table and index I/O, and for table locks.

  • Instrumentation for statements and stages within statements.

  • Configuration of instruments and consumers at server startup, which previously was possible only at runtime.

• MySQL NDB Cluster.  MySQL NDB Cluster is released as a separate product; the most recent GA releases are based on MySQL 5.6 and use version 7.3 of the NDB storage engine. Clustering support is not available in mainline MySQL Server 5.6 releases. For more information about MySQL NDB Cluster 7.3, see Chapter 18, MySQL NDB Cluster 7.3 and NDB Cluster 7.4. The latest current development version is MySQL NDB Cluster 7.4, based on version 7.4 of the NDB storage engine and MySQL Server 5.6. MySQL NDB Cluster 7.4 is currently available for testing and evaluation. The most recent MySQL NDB Cluster 7.4 release can be obtained from https://dev.mysql.com/downloads/cluster/.

  For more information and an overview of improvements made in MySQL NDB Cluster 7.4, see Section 18.1.4.2, “What is New in NDB Cluster 7.4”.

  MySQL NDB Cluster 7.2, the previous GA release, is based on MySQL Server 5.5, and is still available for use in production, although we recommend that new deployments use MySQL NDB Cluster 7.3. For more information about MySQL NDB Cluster 7.2, see MySQL NDB Cluster 7.2.

  MySQL NDB Cluster 7.1 is also still available and supported (although we recommend that new deployments use the latest GA release series, currently MySQL NDB Cluster 7.3). These versions of NDB Cluster are based on MySQL Server 5.1 and documented in the MySQL 5.1 Manual; see https://dev.mysql.com/doc/refman/5.1/en/mysql-cluster.html, for more information.

• Replication and logging.  These replication enhancements were added:

  • MySQL now supports transaction-based replication using global transaction identifiers (also known as “GTIDs”). This makes it possible to identify and track each transaction when it is committed on the originating server and as it is applied by any slaves.

    Enabling of GTIDs in a replication setup is done primarily using the new gtid_mode and enforce_gtid_consistency system variables. For information about additional options and variables introduced in support of GTIDs, see Section 17.1.4.5, “Global Transaction ID Options and Variables”.

    When using GTIDs it is not necessary to refer to log files or positions within those files when starting a new slave or failing over to a new master, which greatly simplifies these tasks. For more information about provisioning servers for GTID replication with or without referring to binary log files, see Section 17.1.3.3, “Using GTIDs for Failover and Scaleout”.

    GTID-based replication is completely transaction-based, which makes it simple to check the consistency of masters and slaves. If all transactions committed on a given master are also committed on a given slave, consistency between the two servers is guaranteed.

    For more complete information about the implementation and use of GTIDs in MySQL Replication, see Section 17.1.3, “Replication with Global Transaction Identifiers”.

  • MySQL row-based replication now supports row image control. By logging only those columns required for uniquely identifying and executing changes on each row (as opposed to all columns) for each row change, it is possible to save disk space, network resources, and memory usage. You can determine whether full or minimal rows are logged by setting the binlog_row_image server system variable to one of the values minimal (log required columns only), full (log all columns), or noblob (log all columns except for unneeded BLOB or TEXT columns). See System Variables Used with Binary Logging, for more information.

  • Binary logs written and read by the MySQL Server are now crash-safe, because only complete events (or transactions) are logged or read back. By default, the server logs the length of the event as well as the event itself and uses this information to verify that the event was written correctly. You can also cause the server to write checksums for the events using CRC32 checksums by setting the binlog_checksum system variable. To cause the server to read checksums from the binary log, use the master_verify_checksum system variable. The --slave-sql-verify-checksum system variable causes the slave SQL thread to read checksums from the relay log.

  • MySQL now supports logging of master connection information and of slave relay log information to tables as well as files. Use of these tables can be controlled independently, by the --master-info-repository and --relay-log-info-repository server options. Setting --master-info-repository to TABLE causes connection information to be logged in the slave_master_info table; setting --relay-log-info-repository to TABLE causes relay log information to be logged to the slave_relay_log_info table. Both of these tables are created automatically, in the mysql system database.

    In order for replication to be resilient to unexpected halts, the slave_master_info and slave_relay_log_info tables must each use a transactional storage engine, and beginning with MySQL 5.6.6, these tables are created using InnoDB for this reason. (Bug #13538891) If you are using a previous MySQL 5.6 release in which both of these tables use MyISAM, this means that, prior to starting replication, you must convert both of them to a transactional storage engine (such as InnoDB) if you wish for replication to be resilient to unexpected halts. You can do this in such cases by means of the appropriate ALTER TABLE ... ENGINE=... statements. You should not attempt to change the storage engine used by either of these tables while replication is actually running.

    See Section 17.3.2, “Handling an Unexpected Halt of a Replication Slave”, for more information.

  • mysqlbinlog now has the capability to back up a binary log in its original binary format. When invoked with the --read-from-remote-server and --raw options, mysqlbinlog connects to a server, requests the log files, and writes output files in the same format as the originals. See Section 4.6.8.3, “Using mysqlbinlog to Back Up Binary Log Files”.

  • MySQL now supports delayed replication such that a slave server deliberately lags behind the master by at least a specified amount of time. The default delay is 0 seconds. Use the new MASTER_DELAY option for CHANGE MASTER TO to set the delay.

    Delayed replication can be used for purposes such as protecting against user mistakes on the master (a DBA can roll back a delayed slave to the time just before the disaster) or testing how the system behaves when there is a lag. See Section 17.3.10, “Delayed Replication”.

  • A replication slave having multiple network interfaces can now be caused to use only one of these (to the exclusion of the others) by using the MASTER_BIND option when issuing a CHANGE MASTER TO statement.

  • The log_bin_basename system variable has been added. This variable contains the complete filename and path to the binary log file. Whereas the log_bin system variable shows only whether or not binary logging is enabled, log_bin_basename reflects the name set with the --log-bin server option.

    Similarly, the relay_log_basename system variable shows the filename and complete path to the relay log file.

  • MySQL Replication now supports parallel execution of transactions with multithreading on the slave. When parallel execution is enabled, the slave SQL thread acts as the coordinator for a number of slave worker threads as determined by the value of the slave_parallel_workers server system variable. The current implementation of multithreading on the slave assumes that data and updates are partitioned on a per-database basis, and that updates within a given database occur in the same relative order as they do on the master. However, it is not necessary to coordinate transactions between different databases. Transactions can then also be distributed per database, which means that a worker thread on the slave can process successive transactions on a given database without waiting for updates to other databases to complete.

    Since transactions on different databases can occur in a different order on the slave than on the master, simply checking for the most recently executed transaction is not a guarantee that all previous transactions on the master have been executed on the slave. This has implications for logging and recovery when using a multithreaded slave. For information about how to interpret binary logging information when using multithreading on the slave, see Section 13.7.5.35, “SHOW SLAVE STATUS Syntax”.

• Optimizer enhancements.  These query optimizer improvements were implemented:

  • The optimizer now more efficiently handles queries (and subqueries) of the following form:

    SELECT ... FROM single_table ... ORDER BY non_index_column [DESC] LIMIT [M,]N;

    That type of query is common in web applications that display only a few rows from a larger result set. For example:

    SELECT col1, ... FROM t1 ... ORDER BY name LIMIT 10;
    SELECT col1, ... FROM t1 ... ORDER BY RAND() LIMIT 15;

    The sort buffer has a size of sort_buffer_size. If the sort elements for N rows are small enough to fit in the sort buffer (M+N rows if M was specified), the server can avoid using a merge file and perform the sort entirely in memory. For details, see Section 8.2.1.16, “LIMIT Query Optimization”.

  • The optimizer implements Disk-Sweep Multi-Range Read. Reading rows using a range scan on a secondary index can result in many random disk accesses to the base table when the table is large and not stored in the storage engine's cache. With the Disk-Sweep Multi-Range Read (MRR) optimization, MySQL tries to reduce the number of random disk access for range scans by first scanning the index only and collecting the keys for the relevant rows. Then the keys are sorted and finally the rows are retrieved from the base table using the order of the primary key. The motivation for Disk-sweep MRR is to reduce the number of random disk accesses and instead achieve a more sequential scan of the base table data. For more information, see Section 8.2.1.10, “Multi-Range Read Optimization”.

  • The optimizer implements Index Condition Pushdown (ICP), an optimization for the case where MySQL retrieves rows from a table using an index. Without ICP, the storage engine traverses the index to locate rows in the base table and returns them to the MySQL server which evaluates the WHERE condition for the rows. With ICP enabled, and if parts of the WHERE condition can be evaluated by using only fields from the index, the MySQL server pushes this part of the WHERE condition down to the storage engine. The storage engine then evaluates the pushed index condition by using the index entry and only if this is satisfied is base row be read. ICP can reduce the number of accesses the storage engine has to do against the base table and the number of accesses the MySQL server has to do against the storage engine. For more information, see Section 8.2.1.5, “Index Condition Pushdown Optimization”.

  • The EXPLAIN statement now provides execution plan information for DELETE, INSERT, REPLACE, and UPDATE statements. Previously, EXPLAIN provided information only for SELECT statements. In addition, the EXPLAIN statement now can produce output in JSON format. See Section 13.8.2, “EXPLAIN Syntax”.

  • The optimizer more efficiently handles subqueries in the FROM clause (that is, derived tables). Materialization of subqueries in the FROM clause is postponed until their contents are needed during query execution, which improves performance. In addition, during query execution, the optimizer may add an index to a derived table to speed up row retrieval from it. For more information, see Section 8.2.2.4, “Optimizing Derived Tables”.

  • The optimizer uses semijoin and materialization strategies to optimize subquery execution. See Section 8.2.2.1, “Optimizing Subqueries with Semijoin Transformations”, and Section 8.2.2.2, “Optimizing Subqueries with Materialization”.

  • A Batched Key Access (BKA) join algorithm is now available that uses both index access to the joined table and a join buffer. The BKA algorithm supports inner join, outer join, and semijoin operations, including nested outer joins and nested semijoins. Benefits of BKA include improved join performance due to more efficient table scanning. For more information, see Section 8.2.1.11, “Block Nested-Loop and Batched Key Access Joins”.

  • The optimizer now has a tracing capability, primarily for use by developers. The interface is provided by a set of optimizer_trace_xxx system variables and the INFORMATION_SCHEMA.OPTIMIZER_TRACE table. For details, see MySQL Internals: Tracing the Optimizer.

• Condition handling.  MySQL now supports the GET DIAGNOSTICS statement. GET DIAGNOSTICS provides applications a standardized way to obtain information from the diagnostics area, such as whether the previous SQL statement produced an exception and what it was. For more information, see Section 13.6.7.3, “GET DIAGNOSTICS Syntax”.

  In addition, several deficiencies in condition handler processing rules were corrected so that MySQL behavior is more like standard SQL:

  • Block scope is used in determining which handler to select. Previously, a stored program was treated as having a single scope for handler selection.

  • Condition precedence is more accurately resolved.

  • Diagnostics area clearing has changed. Bug #55843 caused handled conditions to be cleared from the diagnostics area before activating the handler. This made condition information unavailable within the handler. Now condition information is available to the handler, which can inspect it with the GET DIAGNOSTICS statement. The condition information is cleared when the handler exits, if it has not already been cleared during handler execution.

  • Previously, handlers were activated as soon as a condition occurred. Now they are not activated until the statement in which the condition occurred finishes execution, at which point the most appropriate handler is chosen. This can make a difference for statements that raise multiple conditions, if a condition raised later during statement execution has higher precedence than an earlier condition and there are handlers in the same scope for both conditions. Previously, the handler for the first condition raised would be chosen, even if it had a lower precedence than other handlers. Now the handler for the condition with highest precedence is chosen, even if it is not the first condition raised by the statement.

  For more information, see Section 13.6.7.6, “Scope Rules for Handlers”.

• Data types.  These data type changes have been implemented:

  • MySQL now permits fractional seconds for TIME, DATETIME, and TIMESTAMP values, with up to microseconds (6 digits) precision. See Section 11.3.6, “Fractional Seconds in Time Values”.

  • 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 Section 11.3.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.

  • In MySQL, the TIMESTAMP data type differs in nonstandard ways from other data types in terms of default value and assignment of automatic initialization and update attributes. These behaviors remain the default but now are deprecated, and can be turned off by enabling the explicit_defaults_for_timestamp system variable at server startup. See Section 11.3.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”, and Section 5.1.7, “Server System Variables”.

• Host cache.  MySQL now provides more information about the causes of errors that occur when clients connect to the server, as well as improved access to the host cache, which contains client IP address and host name information and is used to avoid DNS lookups. These changes have been implemented:

  • New Connection_errors_xxx status variables provide information about connection errors that do not apply to specific client IP addresses.

  • Counters have been added to the host cache to track errors that do apply to specific IP addresses, and a new host_cache Performance Schema 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 host cache size now is configurable using the host_cache_size system variable.

  For more information, see Section 8.12.5.2, “DNS Lookup Optimization and the Host Cache”, and Section 22.12.10.1, “The host_cache Table”.

• OpenGIS.  The OpenGIS specification defines functions that test the relationship between two geometry values. MySQL originally implemented these functions such that they used object bounding rectangles and returned the same result as the corresponding MBR-based functions. Corresponding versions are now available that use precise object shapes. These versions are named with an ST_ prefix. For example, Contains() uses object bounding rectangles, whereas ST_Contains() uses object shapes. For more information, see Section 12.16.9, “Functions That Test Spatial Relations Between Geometry Objects”.

Features Deprecated in MySQL 5.6

The following features are deprecated in MySQL 5.6 and may be or will be removed in a future series. Where alternatives are shown, applications should be updated to use them.

For applications that use features deprecated in MySQL 5.6 that have been removed in a higher MySQL series, statements may fail when replicated from a MySQL 5.6 master to a higher-series slave, or may have different effects on master and slave. To avoid such problems, applications that use features deprecated in 5.6 should be revised to avoid them and use alternatives when possible.

• The ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE SQL modes are deprecated and setting the sql_mode value to include any of them generates a warning. In MySQL 5.7, these modes do nothing. Instead, their effects are included in the effects of strict SQL mode (STRICT_ALL_TABLES or STRICT_TRANS_TABLES). The motivation for the change in MySQL 5.7 is to reduce the number of SQL modes with an effect dependent on strict mode and make them part of strict mode itself.

  To make advance preparation for an upgrade to MySQL 5.7, see SQL Mode Changes in MySQL 5.7. That discussion provides guidelines to assess whether your applications will be affected by the SQL mode changes in MySQL 5.7.

• Relying on implicit GROUP BY sorting in MySQL 5.6 is deprecated. To achieve a specific sort order of grouped results, it is preferable to use an explicit ORDER BY clause. GROUP BY sorting is a MySQL extension that may change in a future release; for example, to make it possible for the optimizer to order groupings in whatever manner it deems most efficient and to avoid the sorting overhead.

• Pre-4.1 passwords and the mysql_old_password authentication plugin. 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. However, because pre-4.1 passwords are deprecated, disabling secure_auth is also deprecated.)

  DBAs are advised to convert accounts that use the mysql_old_password authentication plugin to use mysql_native_password instead. For account upgrade instructions, see Section 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

  The OLD_PASSWORD() function generates pre-4.1 password hashes, as does PASSWORD() if the old_passwords system variable is set to 1. OLD_PASSWORD() and old_passwords=1 are deprecated.

• The --skip-innodb option and its synonyms (--innodb=OFF, --disable-innodb, and so forth).

• The innodb_locks_unsafe_for_binlog system variable.

• The date_format, datetime_format, and time_format system variables, which are unused.

• The have_profiling, profiling, and profiling_history_size system variables.

• The innodb_use_sys_malloc and innodb_additional_mem_pool_size system variables.

• The timed_mutexes system variable. It does nothing and has no effect.

• The --language option. Use the --lc-messages-dir and --lc-messages options instead.

• The IGNORE clause for ALTER TABLE. 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).

• The msql2mysql, mysql_convert_table_format, mysql_find_rows, mysql_fix_extensions, mysql_setpermission, mysql_waitpid, mysql_zap, mysqlaccess, and mysqlbug utilities.

• The mysqlhotcopy utility. Alternatives include mysqldump and MySQL Enterprise Backup.

Features Removed in MySQL 5.6

The following items are obsolete and have been removed in MySQL 5.6. Where alternatives are shown, applications should be updated to use them.

For MySQL 5.5 applications that use features removed in MySQL 5.6, statements may fail when replicated from a MySQL 5.5 master to a MySQL 5.6 slave, or may have different effects on master and slave. To avoid such problems, applications that use features removed in MySQL 5.6 should be revised to avoid them and use alternatives when possible.

• The --log server option and the log system variable. Instead, use the general_log system variable to enable the general query log and the general_log_file system variable to set the general query log file name.

• The the log_slow_queries system variable. Instead, use the slow_query_log system variable to enable the slow query log and the slow_query_log_file system variable to set the slow query log file name.

• The --one-thread server option. Use --thread_handling=no-threads instead.

• The --safe-mode server option.

• The --skip-thread-priority server option.

• The --table-cache server option. Use the table_open_cache system variable instead.

• The --init-rpl-role and --rpl-recovery-rank options, the rpl_recovery_rank system variable, and the Rpl_status status variable.

• The engine_condition_pushdown system variable. Use the engine_condition_pushdown flag of the optimizer_switch variable instead.

• The have_csv, have_innodb, have_ndbcluster, and have_partitioning system variables. Use SHOW PLUGINS or query the PLUGINS table in the INFORMATION_SCHEMA database instead.

• The sql_big_tables system variable. Use big_tables instead.

• The sql_low_priority_updates system variable. Use low_priority_updates instead.

• The sql_max_join_size system variable. Use max_join_size instead.

• The max_long_data_size system variable. Use max_allowed_packet instead.

• The FLUSH MASTER and FLUSH SLAVE statements. Use the RESET MASTER and RESET SLAVE statements instead.

• The SLAVE START and SLAVE STOP statements. Use The START SLAVE and STOP SLAVE statements.

• The SHOW AUTHORS and SHOW CONTRIBUTORS statements.

• The OPTION and ONE_SHOT modifiers for the SET statement.

• It is explicitly disallowed to assign the value DEFAULT to stored procedure or function parameters or stored program local variables (for example with a SET var_name = DEFAULT statement). It remains permissible to assign DEFAULT to system variables, as before.

• Most SHOW ENGINE INNODB MUTEX output is removed in 5.6.14. SHOW ENGINE INNODB MUTEX output is removed entirely in MySQL 5.7.2. Comparable information can be generated by creating views on Performance Schema tables.