Dear MySQL users,

MySQL Server 5.5.55 is a new version of the 5.5 production release
of the world's most popular open source database. MySQL 5.5.55 is
recommended for use on production systems.

MySQL 5.5 includes several high-impact enhancements to improve the
performance and scalability of the MySQL Database, taking advantage of
the latest multi-CPU and multi-core hardware and operating systems. In
addition, with release 5.5, InnoDB is now the default storage engine for
the MySQL Database, delivering ACID transactions, referential integrity
and crash recovery by default.

MySQL 5.5 also provides a number of additional enhancements including:

  - Significantly improved performance on Windows, with various
    Windows specific features and improvements
  - Higher availability, with new semi-synchronous replication and
    Replication Heartbeat
  - Improved usability, with Improved index and table partitioning,
    SIGNAL/RESIGNAL support and enhanced diagnostics, including a new
    Performance Schema monitoring capability.

For a more complete look at what's new in MySQL 5.5, please see the
following resources:

MySQL 5.5 is GA, Interview with Tomas Ulin:


If you are running a MySQL production level system, we would like to
direct your attention to MySQL Enterprise Edition, which includes the
most comprehensive set of MySQL production, backup, monitoring,
modeling, development, and administration tools so businesses can
achieve the highest levels of MySQL performance, security and uptime.

For information on installing MySQL 5.5.55 on new servers, please see
the MySQL installation documentation at

For upgrading from previous MySQL releases, please see the important
upgrade considerations at:

MySQL Database 5.5.55 is available in source and binary form for a
number of platforms from our download pages at:

The following section lists the changes in the MySQL source code since
the previous released version of MySQL 5.5. It may also be viewed
online at:


Changes in MySQL 5.5.55 (2017-04-10, General availability)

     * Compilation Notes

     * Configuration Notes

     * Packaging Notes

     * Security Notes

     * Thread Pool Notes

     * Functionality Added or Changed

     * Bugs Fixed

   Compilation Notes

     * Windows builds now use the default runtime libraries
       (builds use the /MD flag). (Bug #25611609)

   Configuration Notes

     * MySQL failed to compile if -DENABLE_DEBUG_SYNC=OFF AND
       -DWITH_DEBUG=ON were both given. The ENABLE_DEBUG_SYNC
       option has been removed and enabling WITH_DEBUG enables
       Debug Sync. (Bug #18374703)

   Packaging Notes

     * Reminder: MySQL 5.5 requires the Microsoft Visual C++
       2008 Redistributable Package to run on Windows platforms.
       Users should make sure the package has been installed on
       the system before starting the server. The package is
       available at the Microsoft Download Center

   Security Notes

     * The mysql_options() C API function now supports a
       MYSQL_OPT_SSL_MODE option. The only permitted option
       value is SSL_MODE_REQUIRED, to require a secure
       connection to the server. It causes mysql_real_connect()
       to fail if an encrypted connection cannot be obtained,
       without falling back to an unencrypted connection. Thus,
       mysql_real_connect() returns an error if the server does
       not support SSL or the client is not configured to use
       SSL. The client/server exchange terminates immediately
       after the initial server packet has been received if the
       server indicates that it does not support SSL.
       To require an encrypted connection in MySQL 5.5, the
       standard MySQL client programs call mysql_options() to
       set MYSQL_OPT_SSL_MODE if the --ssl-mode=REQUIRED
       command-line option was specified. Third-party
       applications that must be able to require encrypted
       connections can use the same technique. For details, see
       The minor C API version number was not incremented for
       this change. Application programs compiled for MySQL 5.5
       that require MYSQL_OPT_SSL_MODE may fail to operate
       properly if the dynamic loader provides an older client
       library without MYSQL_OPT_SSL_MODE. Such applications
       must be written to handle this possibility by checking
       whether the mysql_options() call succeeds or fails. (Bug

   Thread Pool Notes

     * To improve thread_pool plugin performance, connection
       authentication and initialization have been moved from
       the acceptor thread to the thread pool worker threads
       that handle client connections. This enables the acceptor
       thread to handle new connections at a higher rate with
       reduced latency. The INFORMATION_SCHEMA
       TP_THREAD_GROUP_STATE table now contains a
       CONNECT_THREAD_COUNT column that indicates the number of
       threads that are processing or waiting to process
       connection initialization and authentication. There can
       be a maximum of four connection threads per thread group;
       these threads expire after a period of inactivity. (Bug

   Functionality Added or Changed

     * Solaris packages are now marked as dependent on /bin/bash
       because some scripts need features not present in the
       default shell /bin/sh. (Bug #25136289)

     * mysql_secure_installation is more strict about what it
       considers valid yes and no responses. (Bug #13344753, Bug

   Bugs Fixed

     * InnoDB: A server exit on restart was caused by missing
       my_thread_init() and my_thread_exit() functions for
       background threads that initialize the st_my_thread_var
       structure. (Bug #25167032)

     * mysqldump failed to properly quote certain identifiers in
       SQL statements written to the dump output. (Bug

     * For CREATE TABLE statements that specified the table name
       with a database qualifier and included a DATA DIRECTORY
       or INDEX DIRECTORY option, an error occurred if there was
       no default database. (Bug #25514146, Bug #84861)

     * mysqld_safe did not check whether the directory named by
       the --basedir option existed. (Bug #25365194)

     * mysqld_safe failed if the error log file named by the
       --log-error option was a FIFO. (Bug #25356221, Bug

     * mysqld_safe could fail if the --datadir option value
       ended with a / character. (Bug #25319457)

     * A recent change to mysqld_safe caused the mysql.server
       script to be unable to start it if the base directory was
       specified as an absolute path that differed from the
       compiled-in default absolute path. (Bug #25319392, Bug

     * For System V init scripts for RPMs, the [mysqld]
       option-file section was being ignored for some options,
       such as pid-file. (Bug #25287707, Bug #84172)

     * Init scripts failed to launch mysqld_safe if a
       non-default base directory was used. (Bug #25261472, Bug

     * mysqld_safe --no-defaults did not work (inadvertent
       consequence of an earlier bug fix). (Bug #25244898, Bug

     * For a client linked against libmysqlclient, invalid
       memory access could occur during use of prepared
       statements. (Bug #25164932)

     * The fix for Bug #25088048 caused the command used by
       mysqld_safe to start the MySQL server to no longer
       include the mysqld path. (Bug #25144379)
       References: This issue is a regression of: Bug #25088048.

     * Changes made to mysqld_safe in recent MySQL releases
       require the --ledir, --mysqld, --mysqld-version options
       to be specified on the command line; they can no longer
       be specified in option files. This could cause failure of
       init scripts that invoke mysqld_safe. Such scripts now
       pass the value of the MYSQLD_OPTS environment variable as
       the first command-line argument to mysqld_safe, with the
       value set to such command line-only mysqld_safe option
       values as may be required. On platforms that use
       /etc/sysconfig/mysqld, the MYSQLD_OPTS value can be set
       in that file with a line such as this:
MYSQLD_OPTS=" --ledir=/mysqld_ledir --mysqld=my_wrapper "

       The value of MYSQLD_OPTS can also include mysqld options
       for mysqld_safe to pass to mysqld. (Bug #24619033, Bug
       References: This issue is a regression of: Bug #24464380,
       Bug #24483092, Bug #25088048, Bug #25378439, Bug

     * For LOAD DATA used to insert data into an updateable
       view, the check to verify whether a column is actually
       updatable was missing. (Bug #24595937)

     * A regular expression pattern match into a large string
       could result in a server exit due to memory allocation
       failure or integer overflow. (Bug #24449076, Bug

     * An incorrect error was reported for CREATE TABLE
       statements with a large value for the CONNECTION table
       option. The value is now limited to 1024 bytes. (Bug

     * Grant tables with incorrect structure may cause problems
       in user management operations. As a consequence of the
       fix for this, for any operation that modifies a grant
       table, the server now checks whether the table has the
       expected structure and produces an error if not.
       mysql_upgrade must be run to update the tables to the
       expected structure. (Bug #23295423, Bug #25095876, Bug

     * The QUOTE() function could allocate excessive memory. A
       limit of max_allowed_packet bytes is now imposed and
       returns NULL with a warning for attempts to allocate
       more. (Bug #23195404)

     * When attempting to locate the data directory, mysqld_safe
       incorrectly considered $MY_BASEDIR_VERSION/var as one of
       the possible locations. (Bug #23013510, Bug #80866)

     * The main.log_tables-big test case could be unstable on
       highly loaded hosts. Thanks to Laurynas Biveinis for the
       patch. (Bug #22874167, Bug #80607)

     * On non-Linux Unix systems, the mysql.server startup
       script used the Linux command pidof rather than pgrep.
       (Bug #13788154, Bug #64342)

     * Starting multiple instances of mysqld_safe after an
       abnormal server exit could result in one mysqld_safe
       instance killing another. As a consequence of the bug
       fix, the file is no longer used. (Bug
       #11751149, Bug #41908)

     * The --help message for mysqld_safe was corrected to
       mention that the --no-defaults, --defaults-file, and
       --defaults-extra-file options, if given, must be the
       first argument. (Bug #11745176, Bug #11192)

     * The bounds check for the XML parser position stack for
       each level (which has a fixed depth) used the size of the
       array as the upper limit, and so was off by one. This is
       fixed by decreasing the allowable depth by one, which
       actually matches the maximum number of elements in the
       position stack. (Bug #83871, Bug #25111907)
       References: See also: Bug #14040071, Bug #15948580.

On Behalf of MySQL/ORACLE RE Team
Gipson Pulla

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