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 7.5.6, has been released and can be downloaded from

http://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 7.5 is also available from our repository for Linux
platforms, go here for details:

http://dev.mysql.com/downloads/repo/

The release notes are available from

http://dev.mysql.com/doc/relnotes/mysql-cluster/7.5/en/index.html

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

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

Enjoy !


Changes in MySQL NDB Cluster 7.5.6 (5.7.18-ndb-7.5.6) (2017-04-10,
General Availability)

MySQL NDB Cluster 7.5.6 is a new release of MySQL NDB Cluster
7.5, based on MySQL Server 5.7 and including features in
version 7.5 of the NDB
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html)
storage engine, as well as fixing recently discovered bugs in
previous NDB Cluster releases.

Obtaining MySQL NDB Cluster 7.5. MySQL NDB Cluster 7.5
source code and binaries can be obtained from
http://dev.mysql.com/downloads/cluster/.
Repo packages for apt and yum can now be found at
https://dev.mysql.com/downloads/repo/

For an overview of changes made in MySQL NDB Cluster 7.5, see
What is New in MySQL NDB Cluster 7.5
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-what-is-new.html).

This release also incorporates all bugfixes and changes made
in previous NDB Cluster releases, as well as all bugfixes and
feature changes which were added in mainline MySQL 5.7
through MySQL 5.7.18 (see Changes in MySQL 5.7.18 (2017-04-10)
(http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-18.html)).

Platform-Specific Notes

* Ubuntu 14.04 and Ubuntu 16.04 are now supported.

* The minimum required version of Solaris is now Solaris 11
update 3, due to a dependency on system runtime
libraries.

* On Solaris, MySQL is now built with Developer Studio 12.5
instead of gcc. The binaries require the Developer Studio
C/C++ runtime libraries to be installed. See here for how
to install only the libraries:
https://docs.oracle.com/cd/E60778_01/html/E60743/gozsu.html

Functionality Added or Changed

* Packaging: Yum repo packages are added for EL5, EL6, EL7,
and SLES12.
Apt repo packages are added for Debian 7, Debian 8,
Ubuntu 14.04, and Ubuntu 16.04

Bugs Fixed

* Partitioning: The output of EXPLAIN PARTITIONS
(http://dev.mysql.com/doc/refman/5.7/en/explain.html)
displayed incorrect values in the partitions column when
run on an explicitly partitioned NDB
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html)
table having a large number of partitions.
This was due to the fact that, when processing an EXPLAIN
statement, mysqld calculates the partition ID for a hash
value as (hash_value % number_of_partitions), which is
correct only when the table is partitioned by HASH, since
other partitioning types use different methods of mapping
hash values to partition IDs. This fix replaces the
partition ID calculation performed by mysqld with an
internal NDB function which calculates the partition ID
correctly, based on the table's partitioning type. (Bug
#21068548)
References: See also: Bug #25501895, Bug #14672885.

* CPU usage of the data node's main thread by the DBDIH
master block as the end of a local checkpoint could
approach 100% in certain cases where the database had a
very large number of fragment replicas. This is fixed by
reducing the frequency and range of fragment queue
checking during an LCP. (Bug #25443080)

* The ndb_print_backup_file utility failed when attempting
to read from a backup file when the backup included a
table having more than 500 columns. (Bug #25302901)
References: See also: Bug #25182956.

* Multiple data node failures during a partial restart of
the cluster could cause API nodes to fail. This was due
to expansion of an internal object ID map by one thread,
thus changing its location in memory, while another
thread was still accessing the old location, leading to a
segmentation fault in the latter thread.
The internal map() and unmap() functions in which this
issue arose have now been made thread-safe. (Bug
#25092498)
References: See also: Bug #25306089.

* During the initial phase of a scan request, the DBTC
kernel block sends a series of DIGETNODESREQ signals to
the DBDIH block in order to obtain dictionary information
for each fragment to be scanned. If DBDIH returned
DIGETNODESREF, the error code from that signal was not
read, and Error 218 Out of LongMessageBuffer was always
returned instead. Now in such cases, the error code from
the DIGETNODESREF signal is actually used. (Bug #85225,
Bug #25642405)

* There existed the possibility of a race condition between
schema operations on the same database object originating
from different SQL nodes; this could occur when one of
the SQL nodes was late in releasing its metadata lock on
the affected schema object or objects in such a fashion
as to appear to the schema distribution coordinator that
the lock release was acknowledged for the wrong schema
change. This could result in incorrect application of the
schema changes on some or all of the SQL nodes or a
timeout with repeated waiting max ### sec for
distributing... messages in the node logs due to failure
of the distribution protocol. (Bug #85010, Bug #25557263)
References: See also: Bug #24926009.

* When a foreign key was added to or dropped from an NDB
table using an ALTER TABLE
(http://dev.mysql.com/doc/refman/5.7/en/alter-table.html)
statement, the parent table's metadata was not updated,
which made it possible to execute invalid alter
operations on the parent afterwards.
Until you can upgrade to this release, you can work
around this problem by running SHOW CREATE TABLE
(http://dev.mysql.com/doc/refman/5.7/en/show-create-table.html)
on the parent immediately after adding or dropping
the foreign key; this statement causes the table's
metadata to be reloaded. (Bug #82989, Bug #24666177)

* Transactions on NDB
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html)
tables with cascading foreign keys returned
inconsistent results when the query cache was also
enabled, due to the fact that mysqld was not aware of
child table updates. This meant that results for a later
SELECT
(http://dev.mysql.com/doc/refman/5.7/en/select.html) from
the child table were fetched from the query cache, which
at that point contained stale data.
This is fixed in such cases by adding all children of the
parent table to an internal list to be checked by NDB for
updates whenever the parent is updated, so that mysqld is
now properly informed of any updated child tables that
should be invalidated from the query cache. (Bug #81776,
Bug #23553507)

* NDB Disk Data: Stale data from NDB Disk Data tables that
had been dropped could potentially be included in backups
due to the fact that disk scans were enabled for these.
To prevent this possibility, disk scans are now
disabled---as are other types of scans---when taking a
backup. (Bug #84422, Bug #25353234)

* NDB Disk Data: In some cases, setting dynamic in-memory
columns of an NDB Disk Data table to NULL was not handled
correctly. (Bug #79253, Bug #22195588)

* NDB Cluster APIs: When signals were sent while the client
process was receiving signals such as
SUB_GCP_COMPLETE_ACK and TC_COMMIT_ACK, these signals
were temporary buffered in the send buffers of the
clients which sent them. If not explicitly flushed, the
signals remained in these buffers until the client woke
up again and flushed its buffers. Because there was no
attempt made to enforce an upper limit on how long the
signal could remain unsent in the local client buffers,
this could lead to timeouts and other misbehavior in the
components waiting for these signals.
In addition, the fix for a previous, related issue likely
made this situation worse by removing client wakeups
during which the client send buffers could have been
flushed.
The current fix moves responsibility for flushing
messages sent by the receivers, to the receiver
(poll_owner client). This means that it is no longer
necessary to wake up all clients merely to have them
flush their buffers. Instead, the poll_owner client
(which is already running) performs flushing the send
buffer of whatever was sent while delivering signals to
the recipients. (Bug #22705935)
References: See also: Bug #18753341, Bug #23202735.

* CMake now detects whether a GCC 5.3.0 loop optimization
bug occurs and attempts a workaround if so. (Bug
#25253540)


On Behalf of the MySQL RE Team
Lars Tangvald


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