MySQL Cluster 7.4.5 Released

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The binary and source versions of MySQL Cluster 7.4.5 have now been made available at http://www.mysql.com/downloads/cluster/.

Release notes

MySQL Cluster NDB 7.4.5 is a new maintenance release of MySQL Cluster, based on MySQL Server 5.6 and including features from version 7.4 of the NDB storage engine, as well as fixing a number of recently discovered bugs in previous MySQL Cluster releases.

This release also incorporates all bugfixes and changes made in previous MySQL Cluster releases, as well as all bugfixes and feature changes which were added in mainline MySQL 5.6 through MySQL 5.6.23.

Bugs Fixed

  • It was found during testing that problems could arise when the
    node registered as the arbitrator disconnected or failed during
    the arbitration process.

    In this situation, the node requesting arbitration could never
    receive a positive acknowledgement from the registered
    arbitrator; this node also lacked a stable set of members and
    could not initiate selection of a new arbitrator.

    Now in such cases, when the arbitrator fails or loses contact
    during arbitration, the requesting node immediately fails rather
    than waiting to time out.
    (Bug #20538179)

  • DROP DATABASE failed to remove
    the database when the database directory contained a
    .ndb file which had no corresponding table
    in NDB. Now, when executing
    DROP DATABASE, NDB
    performs an check specifically for leftover
    .ndb files, and deletes any that it finds.
    (Bug #20480035)

    References: See also Bug #44529.

  • The maximum failure time calculation used to ensure that normal
    node failure handling mechanisms are given time to handle
    survivable cluster failures (before global checkpoint watchdog
    mechanisms start to kill nodes due to GCP delays) was
    excessively conservative, and neglected to consider that there
    can be at most number_of_data_nodes /
    NoOfReplicas node
    failures before the cluster can no longer survive. Now the value
    of NoOfReplicas is properly taken into
    account when performing this calculation.
    (Bug #20069617, Bug #20069624)

    References: See also Bug #19858151, Bug #20128256, Bug #20135976.

  • During a node restart, if there was no global checkpoint
    completed between the START_LCP_REQ for a
    local checkpoint and its LCP_COMPLETE_REP it
    was possible for a comparison of the LCP ID sent in the
    LCP_COMPLETE_REP signal with the internal
    value SYSFILE->latestLCP_ID to fail.
    (Bug #76113, Bug #20631645)

  • When sending LCP_FRAG_ORD signals as part of
    master takeover, it is possible that the master not is not
    synchronized with complete accuracy in real time, so that some
    signals must be dropped. During this time, the master can send a
    LCP_FRAG_ORD signal with its
    lastFragmentFlag set even after the local
    checkpoint has been completed. This enhancement causes this flag
    to persist until the statrt of the next local checkpoint, which
    causes these signals to be dropped as well.

    This change affects ndbd only; the issue
    described did not occur with ndbmtd.
    (Bug #75964, Bug #20567730)

  • When reading and copying transporter short signal data, it was
    possible for the data to be copied back to the same signal with
    overlapping memory.
    (Bug #75930, Bug #20553247)

  • NDB node takeover code made the assumption that there would be
    only one takeover record when starting a takeover, based on the
    further assumption that the master node could never perform
    copying of fragments. However, this is not the case in a system
    restart, where a master node can have stale data and so need to
    perform such copying to bring itself up to date.
    (Bug #75919, Bug #20546899)

  • Cluster API:
    A scan operation, whether it is a single table scan or a query
    scan used by a pushed join, stores the result set in a buffer.
    This maximum size of this buffer is calculated and preallocated
    before the scan operation is started. This buffer may consume a
    considerable amount of memory; in some cases we observed a 2 GB
    buffer footprint in tests that executed 100 parallel scans with
    2 single-threaded (ndbd) data nodes. This
    memory consumption was found to scale linearly with additional
    fragments.

    A number of root causes, listed here, were discovered that led
    to this problem:

    • Result rows were unpacked to full
      NdbRecord format before
      they were stored in the buffer. If only some but not all
      columns of a table were selected, the buffer contained empty
      space (essentially wasted).

    • Due to the buffer format being unpacked,
      VARCHAR and
      VARBINARY columns always had
      to be allocated for the maximum size defined for such
      columns.

    • BatchByteSize and
      MaxScanBatchSize
      values were not taken into consideration as a limiting
      factor when calculating the maximum buffer size.

    These issues became more evident in NDB 7.2 and later MySQL
    Cluster release series. This was due to the fact buffer size is
    scaled by BatchSize, and
    that the default value for this parameter was increased fourfold
    (from 64 to 256) beginning with MySQL Cluster NDB 7.2.1.

    This fix causes result rows to be buffered using the packed
    format instead of the unpacked format; a buffered scan result
    row is now not unpacked until it becomes the current row. In
    addition, BatchByteSize and
    MaxScanBatchSize are now used as limiting
    factors when calculating the required buffer size.

    Also as part of this fix, refactoring has been done to separate
    handling of buffered (packed) from handling of unbuffered result
    sets, and to remove code that had been unused since NDB 7.0 or
    earlier. The NdbRecord class declaration has
    also been cleaned up by removing a number of unused or redundant
    member variables.
    (Bug #73781, Bug #75599, Bug #19631350, Bug #20408733)

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