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MySQL Cluster 7.6.15 has been released
Posted by: Piotr Obrzut
Date: July 14, 2020 01:57AM

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 7.6.15 has been released and can be downloaded from

https://www.mysql.com/downloads/cluster/

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:

https://dev.mysql.com/downloads/

The release notes are available from

https://dev.mysql.com/doc/relnotes/mysql-cluster/7.6/en/

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

https://www.mysql.com/products/cluster/

Enjoy !

==============================================================================

Changes in MySQL NDB Cluster 7.6.15 (5.7.31-ndb-7.6.15) (2020-07-14, General Availability)

MySQL NDB Cluster 7.6.15 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
https://dev.mysql.com/downloads/cluster/.

For an overview of changes made in NDB Cluster 7.6, see What
is New in NDB Cluster 7.6
(https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-what-is-new-7-6.html).

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 5.7.31 (see Changes in MySQL 5.7.31 (2020-07-13, General Availability)
(https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-31.html)).

Bugs Fixed


* NDB Disk Data: ndbmtd sometimes terminated unexpectedly
when it could not complete a lookup for a log file group
during a restore operation. (Bug #31284086)

* NDB Disk Data: An uninitialized variable led to issues
when performing Disk Data DDL operations following a
restart of the cluster. (Bug #30592528)

* ndb_restore --remap-column did not handle columns
containing NULL values correctly. Now any offset
specified by the mapping function used with this option
is not applied to NULL, so that NULL is preserved as
expected. (Bug #31966676)

* MaxDiskWriteSpeedOwnRestart was not honored as an upper
bound for local checkpoint writes during a node restart.
(Bug #31337487)
References: See also: Bug #29943227.

* During a node restart, the SUMA block of the node that is
starting must get a copy of the subscriptions (events
with subscribers) and subscribers (NdbEventOperation
instances which are executing) from a node already
running. Before the copy is complete, nodes which are
still starting ignore any user-level SUB_START or
SUB_STOP requests; after the copy is done, they can
participate in such requests. While the copy operation is
in progress, user-level SUB_START and SUB_STOP requests
are blocked using a DICT lock.
An issue was found whereby a starting node could
participate in SUB_START and SUB_STOP requests after the
lock was requested, but before it is granted, which
resulted in unsuccessful SUB_START and SUB_STOP requests.
This fix ensures that the nodes cannot participate in
these requests until after the DICT lock has actually
been granted. (Bug #31302657)

* DUMP 1001 (DumpPageMemoryOnFail) now prints out
information about the internal state of the data node
page memory manager when allocation of pages fails due to
resource constraints. (Bug #31231286)

* Statistics generated by NDB for use in tracking internal
objects allocated and deciding when to release them were
not calculated correctly, with the result that the
threshold for resource usage was 50% higher than
intended. This fix corrects the issue, and should allow
for reduced memory usage. (Bug #31127237)

* An excessive number of entries were written to the backup
log when performing an online backup, using ndbmtd on the
data nodes. This happened because row changes occurring
to fragments managed by LDM instance 1 were always
recorded in the log, even when they were for primary
fragments other than primary fragments. This wasted
resources when restoring from the backup, and could cause
other problems when doing so, such as when using staging
tables for schema transforms while executing ndb_restore.
(Bug #31034270)

* The Dojo toolkit included with NDB Cluster and used by
the Auto-Installer was upgraded to version 1.15.3. (Bug
#31029110)

* A packed version 1 configuration file returned by
ndb_mgmd could contain duplicate entries following an
upgrade to NDB 8.0, which made the file incompatible with
clients using version 1. This occurs due to the fact that
the code for handling backwards compatibility assumed
that the entries in each section were already sorted when
merging it with the default section. To fix this, we now
make sure that this sort is performed prior to merging.
(Bug #31020183)

* When executing any of the SHUTDOWN, ALL STOP, or ALL
RESTART management commands, it is possible for different
nodes to attempt to stop on different global checkpoint
index (CGI) boundaries. If they succeed in doing so, then
a subsequent system restart is slower than normal because
any nodes having an earlier stop GCI must undergo
takeover as part of the process. When nodes failing on
the first GCI boundary cause surviving nodes to be
nonviable, surviving nodes suffer an arbitration failure;
this has the positive effect of causing such nodes to
halt at the correct GCI, but can give rise to spurious
errors or similar.
To avoid such issues, extra synchronization is now
performed during a planned shutdown to reduce the
likelihood that different data nodes attempt to shut down
at different GCIs as well as the use of unnecessary node
takeovers during system restarts. (Bug #31008713)

* When responding to a SCANTABREQ, an API node can provide
a distribution key if it knows that the scan should work
on only one fragment, in which case the distribution key
should be the fragment ID, but in some cases a hash of
the partition key was used instead, leading to failures
in DBTC. (Bug #30774226)

* Several memory leaks found in ndb_import have been
removed. (Bug #30756434, Bug #30727956)

* The master node in a backup shut down unexpectedly on
receiving duplicate replies to a DEFINE_BACKUP_REQ
signal. These occurred when a data node other than the
master errored out during the backup, and the backup
master handled the situation by sending itself a
DEFINE_BACKUP_REF signal on behalf of the missing node,
which resulted in two replies being received from the
same node (a CONF signal from the problem node prior to
shutting down and the REF signal from the master on
behalf of this node), even though the master expected
only one reply per node. This scenario was also
encountered for START_BACKUP_REQ and STOP_BACKUP_REQ
signals.
This is fixed in such cases by allowing duplicate replies
when the error is the result of an unplanned node
shutdown. (Bug #30589827)

* When updating NDB_TABLE comment options using ALTER
TABLE, other options which has been set to non-default
values when the table was created but which were not
specified in the ALTER TABLE statement could be reset to
their defaults.
See Setting NDB_TABLE Options
(https://dev.mysql.com/doc/refman/5.7/en/create-table-ndb-table-comment-options.html),
for more information. (Bug #30428829)

* When, during a restart, a data node received a
GCP_SAVEREQ signal prior to beginning start phase 9, and
thus needed to perform a global checkpoint index write to
a local data manager's local checkpoint control file, it
did not record information from the DIH block originating
with the node that sent the signal as part of the data
written. This meant that, later in start phase 9, when
attempting to send a GCP_SAVECONF signal in response to
the GCP_SAVEREQ, this information was not available,
which meant the response could not be sent, resulting in
an unplanned shutdown of the data node. (Bug #30187949)

* Setting EnableRedoControl to false did not fully disable
MaxDiskWriteSpeed, MaxDiskWriteSpeedOtherNodeRestart, and
MaxDiskWriteSpeedOwnRestart as expected. (Bug #29943227)
References: See also: Bug #31337487.

* Removed a memory leak found in the ndb_import utility.
(Bug #29820879)

* A BLOB value is stored by NDB in multiple parts; when
reading such a value, one read operation is executed per
part. If a part is not found, the read fails with a row
not found error, which indicates a corrupted BLOB, since
a BLOB should never have any missing parts. A problem can
arise because this error is reported as the overall
result of the read operation, which means that mysqld
sees no error and reports zero rows returned.
This issue is fixed by adding a check specifically for
the case in wich a blob part is not found. Now, when this
occurs, overwriting the row not found error with
corrupted blob, which causes the originating SELECT
statement to fail as expected. Users of the NDB API
should be aware that, despite this change, the
NdbBlob::getValue() method continues to report the error
as row not found in such cases. (Bug #28590428)

* Incorrect handling of operations on replicas during node
restarts could result in a forced shutdown, or in content
diverging between replicas, when primary keys with
nonbinary (case-sensitive) equality conditions were used.
(Bug #98526, Bug #30884622)

On Behalf of MySQL Release Engineering Team
Piotr Obrzut

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MySQL Cluster 7.6.15 has been released
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