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MySQL Cluster 7.6.8 has been released
Posted by: Lars Tangvald
Date: October 23, 2018 11:46AM

Dear MySQL Users,

MySQL Cluster is the distributed, shared-nothing variant of MySQL.
This storage engine provides:

  - In-Memory storage - Real-time performance (with optional
    checkpointing to disk)
  - Transparent Auto-Sharding - Read & write scalability
  - Active-Active/Multi-Master geographic replication

  - 99.999% High Availability with no single point of failure
    and on-line maintenance
  - NoSQL and SQL APIs (including C++, Java, http, Memcached
    and JavaScript/Node.js)

MySQL Cluster 7.6.8, has been released and can be downloaded from

where you will also find Quick Start guides to help you get your
first MySQL Cluster database up and running.

MySQL Cluster 7.6 is also available from our repository for Linux
platforms, go here for details:

The release notes are available from

MySQL Cluster enables users to meet the database challenges of next
generation web, cloud, and communications services with uncompromising
scalability, uptime and agility.

More details can be found at

Enjoy !

Changes in MySQL NDB Cluster 7.6.8 (5.7.24-ndb-7.6.8) (2018-10-23, General Availability)

   MySQL NDB Cluster 7.6.8 is a new release of NDB 7.6, based on
   MySQL Server 5.7 and including features in version 7.6 of the
   NDB storage engine, as well as fixing recently discovered
   bugs in previous NDB Cluster releases.

   Obtaining NDB Cluster 7.6.  NDB Cluster 7.6 source code and
   binaries can be obtained from

   For an overview of changes made in NDB Cluster 7.6, see What
   is New in NDB Cluster 7.6

   This release also incorporates all bug fixes and changes made
   in previous NDB Cluster releases, as well as all bug fixes
   and feature changes which were added in mainline MySQL 5.7
   through MySQL 5.7.24 (see Changes in MySQL 5.7.24 (2018-10-22, General Availability)

Functionality Added or Changed

     * Performance: This release introduces a number of
       significant improvements in the performance of scans;
       these are listed here:

          + Row checksums help detect hardware issues, but do so
            at the expense of performance. NDB now offers the
            possibility of disabling these by setting the new
            ndb_row_checksum server system variable to 0; doing
            this means that row checksums are not used for new
            or altered tables. This can have a significant
            impact (5 to 10 percent, in some cases) on
            performance for all types of queries. This variable
            is set to 1 by default, to provide compatibility
            with the previous behavior.

          + A query consisting of a scan can execute for a
            longer time in the LDM threads when the queue is not

          + Previously, columns were read before checking a
            pushed condition; now checking of a pushed condition
            is done before reading any columns.

          + Performance of pushed joins should see significant
            improvement when using range scans as part of join

Bugs Fixed

     * Packaging: Expected NDB header files were in the devel
       RPM package instead of libndbclient-devel. (Bug #84580,
       Bug #26448330)

     * NDB Disk Data: While restoring a local checkpoint, it is
       possible to insert a row that already exists in the
       database; this is expected behavior which is handled by
       deleting the existing row first, then inserting the new
       copy of that row. In some cases involving data on disk,
       NDB failed to delete the existing row. (Bug #91627, Bug

     * NDB Client Programs: Removed a memory leak in
       NdbImportUtil::RangeList that was revealed in ASAN
       builds. (Bug #91479, Bug #28264144)

     * MySQL NDB ClusterJ: When a table containing a BLOB or a
       TEXT field was being queried with ClusterJ for a record
       that did not exist, an exception ("The method is not
       valid in current blob state") was thrown. (Bug #28536926)

     * MySQL NDB ClusterJ: A NullPointerException was thrown
       when a full table scan was performed with ClusterJ on
       tables containing either a BLOB or a TEXT field. It was
       because the proper object initializations were omitted,
       and they have now been added by this fix. (Bug #28199372,
       Bug #91242)

     * When copying deleted rows from a live node to a node just
       starting, it is possible for one or more of these rows to
       have a global checkpoint index equal to zero. If this
       happened at the same time that a full local checkpoint
       was started due to the undo log getting full, the
       LCP_SKIP bit was set for a row having GCI = 0, leading to
       an unplanned shutdown of the data node. (Bug #28372628)

     * ndbmtd sometimes experienced a hang when exiting due to
       log thread shutdown. (Bug #28027150)

     * When the SUMA kernel block receives a SUB_STOP_REQ
       signal, it executes the signal then replies with
       SUB_STOP_CONF. (After this response is relayed back to
       the API, the API is open to send more SUB_STOP_REQ
       signals.) After sending the SUB_STOP_CONF, SUMA drops the
       subscription if no subscribers are present, which
       involves sending multiple DROP_TRIG_IMPL_REQ messages to
       DBTUP. LocalProxy can handle up to 21 of these requests
       in parallel; any more than this are queued in the Short
       Time Queue. When execution of a DROP_TRIG_IMPL_REQ was
       delayed, there was a chance for the queue to become
       overloaded, leading to a data node shutdown with Error in
       short time queue.
       This issue is fixed by delaying the execution of the
       SUB_STOP_REQ signal if DBTUP is already handling
       DROP_TRIG_IMPL_REQ signals at full capacity, rather than
       queueing up the DROP_TRIG_IMPL_REQ signals. (Bug

     * Having a large number of deferred triggers could
       sometimes lead to job buffer exhaustion. This could occur
       due to the fact that a single trigger can execute many
       operations---for example, a foreign key parent trigger
       may perform operations on multiple matching child table
       rows---and that a row operation on a base table can
       execute multiple triggers. In such cases, row operations
       are executed in batches. When execution of many triggers
       was deferred---meaning that all deferred triggers are
       executed at pre-commit---the resulting concurrent
       execution of a great many trigger operations could cause
       the data node job buffer or send buffer to be exhausted,
       leading to failure of the node.
       This issue is fixed by limiting the number of concurrent
       trigger operations as well as the number of trigger fire
       requests outstanding per transaction.
       For immediate triggers, limiting of concurrent trigger
       operations may increase the number of triggers waiting to
       be executed, exhausting the trigger record pool and
       resulting in the error Too many concurrently fired
       triggers (increase MaxNoOfFiredTriggers. This can be
       avoided by increasing MaxNoOfFiredTriggers, reducing the
       user transaction batch size, or both. (Bug #22529864)
       References: See also: Bug #18229003, Bug #27310330.

     * ndbout and ndberr became invalid after exiting from
       mgmd_run(), and redirecting to them before the next call
       to mgmd_run() caused a segmentation fault, during an mgmd
       service restart. This fix ensures that ndbout and ndberr
       remain valid at all times. (Bug #17732772, Bug #28536919)

     * Running out of undo log buffer memory was reported using
       error 921 Out of transaction memory ... (increase
       This problem is fixed by introducing a new error code 923
       Out of undo buffer memory (increase UNDO_BUFFER_SIZE).
       (Bug #92125, Bug #28537319)

     * When moving an OperationRec from the serial to the
       parallel queue, Dbacc::startNext() failed to update the
       Operationrec::OP_ACC_LOCK_MODE flag which is required to
       reflect the accumulated OP_LOCK_MODE of all previous
       operations in the parallel queue. This inconsistency in
       the ACC lock queues caused the scan lock takeover
       mechanism to fail, as it incorrectly concluded that a
       lock to take over was not held. The same failure caused
       an assert when aborting an operation that was a member of
       such an inconsistent parallel lock queue. (Bug #92100,
       Bug #28530928)

     * A data node failed during startup due to the arrival of a
       SCAN_FRAGREQ signal during the restore phase. This signal
       originated from a scan begun before the node had
       previously failed and which should have been aborted due
       to the involvement of the failed node in it. (Bug #92059,
       Bug #28518448)

     * DBTUP sent the error Tuple corruption detected when a
       read operation attempted to read the value of a tuple
       inserted within the same transaction. (Bug #92009, Bug

     * False constraint violation errors could occur when
       executing updates on self-referential foreign keys. (Bug
       #91965, Bug #28486390)
       References: See also: Bug #90644, Bug #27930382.

     * An NDB internal trigger definition could be dropped while
       pending instances of the trigger remained to be executed,
       by attempting to look up the definition for a trigger
       which had already been released. This caused
       unpredictable and thus unsafe behavior possibly leading
       to data node failure. The root cause of the issue lay in
       an invalid assumption in the code relating to determining
       whether a given trigger had been released; the issue is
       fixed by ensuring that the behavior of NDB, when a
       trigger definition is determined to have been released,
       is consistent, and that it meets expectations. (Bug
       #91894, Bug #28451957)

     * In some cases, a workload that included a high number of
       concurrent inserts caused data node failures when using
       debug builds. (Bug #91764, Bug #28384750)

     * During an initial node restart with disk data tables
       present and TwoPassInitialNodeRestartCopy enabled, DBTUP
       used an unsafe scan in disk order. Such scans are no
       longer employed in this case. (Bug #91724, Bug #28378227)

     * Checking for old LCP files tested the table version, but
       this was not always dependable. Now, instead of relying
       on the table version, the check reagrds as invalid any
       LCP file having a maxGCI smaller than its createGci. (Bug
       #91637, Bug #28346565)

     * In certain cases, a cascade update trigger was fired
       repeatedly on the same record, which eventually consumed
       all available concurrent operations, leading to Error 233
       Out of operation records in transaction coordinator
       (increase MaxNoOfConcurrentOperations). If
       MaxNoOfConcurrentOperations was set to a value
       sufficiently high to avoid this, the issue manifested as
       data nodes consuming very large amounts of CPU, very
       likely eventually leading to a timeout. (Bug #91472, Bug

     * Inserting a row into an NDB table having a
       self-referencing foreign key that referenced a unique
       index on the table other than the primary key failed with
       ER_NO_REFERENCED_ROW_2. This was due to the fact that NDB
       checked foreign key constraints before the unique index
       was updated, so that the constraint check was unable to
       use the index for locating the row. Now, in such cases,
       NDB waits until all unique index values have been updated
       before checking foreign key constraints on the inserted
       row. (Bug #90644, Bug #27930382)
       References: See also: Bug #91965, Bug #28486390.

     * A connection string beginning with a slash (/) character
       is now rejected by ndb_mgmd.
       Our thanks to Daniƫl van Eeden for contributing this fix.
       (Bug #90582, Bug #27912892)

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Written By
MySQL Cluster 7.6.8 has been released
October 23, 2018 11:46AM

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