Changes in MySQL 5.6.42
Functionality Added or Changed
* Previously, file I/O performed in the I/O cache in the mysys library was not instrumented, affecting in particular file I/O statistics reported by the Performance Schema about the binary log index file. Now, this I/O is instrumented and Performance Schema statistics are accurate. Thanks to Yura Sorokin for the contribution.
* 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.
* The zlib compressBound() function in zlib 1.2.11 returns a slightly higher estimate of the buffer size required to compress a given length of bytes than it did in zlib version 1.2.3. The compressBound() function is called by InnoDB functions that determine the maximum row size permitted when creating compressed InnoDB tables or inserting rows into compressed InnoDB tables. As a result, CREATE TABLE ... ROW_FORMAT=COMPRESSED or INSERT operations with row sizes very close to the maximum row size that were successful in earlier releases could now fail.
Bugs Fixed
* InnoDB: An ALTER TABLE operation that added a primary key produced a segmentation fault.
* InnoDB: An assertion was raised during an OPTIMIZE TABLE operation.
* InnoDB: A foreign key constraint name was duplicated during a rename table operation, causing a failure during later query execution.
* InnoDB: The location of the Innodb Merge Temp File that reported by the wait/io/file/innodb/innodb_temp_file Performance Schema instrument was incorrect.
* Replication: When FLUSH statements for specific log types (such as FLUSH SLOW LOGS) resulted in an error, the statements were still written to the binary log. This stopped replication because the error had occurred on the master, but did not occur on the slave. MySQL Server now checks on the outcome of these FLUSH statements, and if an error occurred, the statement is not written to the binary log.
* Microsoft Windows: On Windows, uninstallation of the MySQL Server MSI package through MySQL Installer produced a spurious popup window.
* Concurrent INSERT and SELECT statements on a MERGE table could result in a server exit.
* MySQL Server and test RPM packages were missing perl-Data-Dumper as a dependency.
* For the mysql client, the -b short option was associated with two long options, --no-beep and --binary-as-hex. The -b option now is associated only with --no-beep.
* Very long table keys were handled incorrectly on replication slaves.
* During server startup/shutdown, PID files could be mishandled.
* For MEMORY tables, memory overflow errors could occur.
* When converting from a BLOB (or TEXT) type to a smaller BLOB (or TEXT) type, no warning or error was reported informing about the truncation or data loss. Now an appropriate error is issued in strict SQL mode and a warning in nonstrict SQL mode.
* Failure to create a temporary table during a MyISAM query could cause a server exit. Thanks to Facebook for the patch.
* An attempted read of an uncommitted transaction raised an assertion.
* ALTER TABLE ... REORGANIZE PARTITION ... could result in incorrect behavior if any partition other than the last was missing the VALUES LESS THAN part of the syntax.
* yum update did not properly update from RHEL5 RPM packages to current packages.
* It was possible for a subquery that used a unique key on a column allowing NULL to return multiple rows.
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