Changes in MySQL 5.7.25
Deprecation and Removal Notes
The resolveip and resolve_stack_dump utilities are now deprecated and will be removed in MySQL 8.0. nslookup, host, or dig can be used instead of resolveip. Stack traces from official MySQL builds are always symbolized, so there is no need to use resolve_stack_dump.
Pluggable Authentication
If the LDAP port number is configured as 636 or 3269, the plugin now uses LDAPS (LDAP over SSL) instead of LDAP. The port number is settable using the authentication_ldap_sasl_server_port or authentication_ldap_simple_server_port system variable. (LDAPS differs from startTLS.)
Previously, for LDAP authentication with proxying, LDAP authentication plugins used the first group name returned by the LDAP server as the MySQL proxy user account name. The authentication string for a MySQL account now can specify a list of groups to match, in preference order, and can optionally map the matching group name to a specified MySQL proxy user name. See LDAP Pluggable Authentication.
Security Notes
The linked OpenSSL library for the MySQL Commercial Server has been updated to version 1.0.2q. Issues fixed in the new OpenSSL version are described at http://www.openssl.org/news/vulnerabilities.html.
This change does not affect the Oracle-produced MySQL Community build of MySQL Server, which uses the yaSSL library instead.
Functionality Added or Changed
Microsoft Windows: The access control granted to clients on the named pipe created by the MySQL server now is set 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 server 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.
Bugs Fixed
InnoDB: A dangling pointer caused a memory leak.
InnoDB: An ON DELETE CASCADE operation on table with a foreign key constraint and an indexed virtual column caused the server to exit.
InnoDB: An incorrectly written DML log involving a virtual column value raised an assertion.
InnoDB: Using the O_DIRECT_NO_FSYNC innodb_flush_method setting could cause the system to hang due to file system metadata becoming unsynchronized. To prevent this issue from occurring in O_DIRECT_NO_FSYNC mode, InnoDB now calls fsync() after creating a new file, after increasing file size, and after closing a file. The fsync() system call is still skipped after each write operation.
With the changes described above, O_DIRECT_NO_FSYNC mode can now be safely used on EXT4 and XFS file systems.
InnoDB: An assertion was raised when attempting to write to a tablespace file greater than 4GB in size on a 64-bit Windows system. The failure was due to a narrowing cast.
Partitioning: Repeated ALTER TABLE statements on partitioned tables containing BLOB or TEXT columns were not always handled correctly.
Partitioning: ALTER TABLE ... EXCHANGE PARTITION did not work when the partitioned table had one or more partition definitions using the DATA DIRECTORY option. This fix supports partitioned tables using the InnoDB storage engine only.
Replication: A patch to correct the handling of quotes for identifiers in ROLLBACK TO SAVEPOINT statements in the binary log was not correctly applied to subsequent MySQL versions.
Replication: Following a patch in MySQL 5.7.23, LOAD DATA statements stopped statement-based replication from a MySQL 5.7.22 master to a replication slave at a later release. The problem has now been fixed.
Replication: In some circumstances, the CHANGE MASTER TO statement could not be used on a replication slave if the master info log had been changed from a table (master_info_repository=TABLE) into a file (master_info_repository=FILE).
Replication: When the system variables binlog_transaction_dependency_tracking and binlog_transaction_dependency_history_size were set or read, the types of lock that were required could result in a deadlock scenario, because the same locks were also required for working with the active binary logs. A new lock type is now used instead for access to the transaction dependency tracking system variables, so that this deadlock cannot occur.
Replication: The PURGE BINARY LOGS TO 'log_name' statement failed for binary log files that had been moved to another location using mysqlbinlogmove. Such files are still listed in the binary log index file, but they are listed using an absolute path, rather than a path relative to the directory where the binary log files are normally stored. MySQL Server can now locate and purge moved binary log files successfully.
Replication: If autocommit was set to 0 for a replication slave or Group Replication group member where GTIDs were in use and super_read_only=ON was set, server shutdown was prevented by a transaction that did not complete. The transaction was attempting to save GTIDs to the mysql.gtid_executed table, but the update failed because super_read_only=ON was set. (With autocommit set to 1, the transaction would complete in this situation, and the mysql.gtid_executed table would instead be updated at server startup.) Now, the check for the super_read_only setting is skipped for this task, so the transaction is able to save the GTIDs to the mysql.gtid_executed table and complete regardless of the combination of super_read_only and autocommit settings.
Replication: An assertion was raised in debug builds if an XA ROLLBACK statement was issued for an unknown transaction identifier when the gtid_next value had been set manually. The server now does not attempt to update the GTID state if an XA ROLLBACK statement fails with an error.
Replication: The value returned by a SHOW SLAVE STATUS statement for the total combined size of all existing relay log files (Relay_Log_Space) could become much larger than the actual disk space used by the relay log files. The I/O thread did not lock the variable while it updated the value, so the SQL thread could automatically delete a relay log file and write a reduced value before the I/O thread finished updating the value. The I/O thread then wrote its original size calculation, ignoring the SQL thread's update and so adding back the space for the deleted file. The Relay_Log_Space value is now locked during updates to prevent concurrent updates and ensure an accurate calculation.
Replication: If the relay log index file was temporarily locked for viewing by a backup process for a replication slave, and MySQL Server also attempted to access the file at that time for rename or delete operations, the backup completed with warnings, but MySQL Server experienced an unexpected halt. MySQL Server now retries the file access operation a number of times in case this or a similar scenario is the explanation and the file becomes available again before long.
Replication: With sync_binlog=1 set, if the binary log was rotated during a commit before the binary log end position was updated, replication stopped on the slave because the server attempted to use the old binary log end position with the new binary log file. The server now compares the binary log file name with the active binary log file when updating the binary log end position, so that the issue does not occur.
Replication: When adding a new member to a group, if the certification information was too big to transmit, an event was generated that caused failures in all group members. To avoid this situation, now if the certification information is too large an error is generated which makes the joining member leave the group.
Replication: When stopping replication, any channels that had pending transactions could cause a deadlock in Group Replication.
The keyring_aws plugin was missing from Commercial packages for macOS.
The supported macOS versions for this plugin now are macOS 10.13 and 10.14.
MySQL Enterprise Firewall did not work well if the audit_log plugin was installed.
The server permitted creation of databases with the same name as redo log files, which could result in unexpected server behavior. Such names are no longer permitted as database names.
Removal of Sun RPC and XDR from glibc into a separate libtirpc library caused problems with libasan on some platforms.
In LDAP group search filter values, special characters were not escaped. Special characters in the user DN now are escaped with their hexadecimal equivalant as follows:
* => \2a
( => \28
) => \29
\ => \5c
\0 => \00
A memory leak was caused by GET_LOCK() calls with a zero timeout that failed due to concurrent connections holding the same user-level lock.
mysqlpump did not free all allocated resources when it encountered an error, resulting in memory leaks.
For debug builds, the server could exit when attempting to roll back CREATE USER statements.
Mishandling of deprecated system variables could cause output from queries on the Performance Schema variables_by_thread table to be incorrect.
When a subquery contained a UNION, the count of the number of subquery columns was calculated incorrectly.
On a GTID-enabled server, concurrent statements on the INFORMATION_SCHEMA.COLUMNS table could deadlock.
Comparing log file names as strings using the memcmp() function resulted in uninitialized memory read errors. The comparison now uses the strncmp() function. Thanks to Zsolt Parragi and Laurynas Biveinis for their contributions.
The optimizer skipped the second column in a composite index when executing an inner join with a LIKE clause against the second column.
CREATE TABLE ... SELECT could create date columns with “zero” date default values when it should have created them without a default value.
The transformation of IN subquery predicates into semijoins was not handled correctly for a very large number of tables.
Server mishandling of SIGHUP signals could result in a server exit.
When the character set of one string comparison operand was a superset of the character set of the other operand, some comparisons were disallowed that should be permitted by converting the operand with the “smaller” character set to the “larger” character set. utf8mb4 and utf32 are considered to be a superset of any other encoding.
Improper memory handling by account management statements could result in server misbehavior.
Executing a prepared statement to do a multiple-row insert with large number of placeholders consumed excessive memory and could execute slowly.
The parser accepted invalid SET statement syntax in trigger definitions that could result in a server exit.
The server failed to start if the keyring_encrypted_file plugin keyring file was invalid.
Keyring migration failed with source and destination keyring plugins of keyring_okv and keyring_encrypted_file, respectively.
When executing a prepared statement with a procedure call with the CURSOR_TYPE_READ_ONLY flag set, the client library hung if the procedure performed a SELECT that returned an empty result set.
The parser performed some out-of-memory checks incorrectly.
When binlog_format is ROW or MIXED, operations on temporary tables are not logged. Previously, the exception to this rule was that when the connection was terminated at the end of the session, the statement DROP TEMPORARY TABLE IF EXISTS was logged for any temporary tables that had been opened in the session. For row-based replication, this behavior caused an unnecessary write to the binary log, and added a transaction sequence number for the GTID where these were enabled.
Now, when a temporary table is created in a session, the binary logging format is tracked. The DROP TEMPORARY TABLE IF EXISTS statement is only logged at the end of the session if statement-based format was in effect when the temporary table was created, so the CREATE TEMPORARY TABLE statement was logged. If row-based or mixed-format binary logging was in use when the table was created, the DROP TEMPORARY TABLE IF EXISTS statement is not logged.
Thanks to Laurynas Biveinis for the patch.
DML statements using IGNORE were not always handled correctly on tables having generated columns.
A query employing a dynamic range and an index merge could use more memory than expected.
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