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 7.5.2 DMR, 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.

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 Cluster NDB 7.5.2 (5.7.12-ndb-7.5.2) (2016-06-01,
Developer Milestone 3)

MySQL Cluster NDB 7.5.2 is a new release of MySQL 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 MySQL Cluster releases.

Obtaining MySQL Cluster NDB 7.5. MySQL Cluster NDB 7.5
source code and binaries can be obtained from
http://dev.mysql.com/downloads/cluster/.

For an overview of changes made in MySQL Cluster NDB 7.5, see
What is New in MySQL Cluster NDB 7.5
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-what-is
-new.html
<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 MySQL Cluster releases, as well as all bugfixes
and feature changes which were added in mainline MySQL 5.7
through MySQL 5.7.12 (see Changes in MySQL 5.7.12
(2016-04-11)
(http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-12.h
tml <http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-12.html>)).


Bugs Fixed

* Performance: A performance problem was found in an
internal polling method do_poll() where the polling
client did not check whether it had itself been woken up
before completing the poll. Subsequent analysis showed
that it is sufficient that only some clients in the
polling queue receive data. do_poll() can then signal
these clients and give up its polling rights, even if the
maximum specified wait time (10 ms) has not expired.
This change allows do_poll() to continue polling until
either the maximum specified wait time has expired, or
the polling client itself has been woken up (by receiving
what it was waiting for). This avoids unnecessary thread
switches between client threads and thus reduces the
associated overhead by as much as 10% in the API client,
resulting in a significant performance improvement when
client threads perform their own polling. (Bug #81229,
Bug #23202735)

* Incompatible Change: When the data nodes are only
partially connected to the API nodes, a node used for a
pushdown join may get its request from a transaction
coordinator on a different node, without (yet) being
connected to the API node itself. In such cases, the
NodeInfo object for the requesting API node contained no
valid info about the software version of the API node,
which caused the DBSPJ block to assume (incorrectly) when
aborting to assume that the API node used NDB version
7.2.4 or earlier, requiring the use of a backward
compatability mode to be used during query abort which
sent a node failure error instead of the real error
causing the abort.
Now, whenever this situation occurs, it is assumed that,
if the NDB software version is not yet available, the API
node version is greater than 7.2.4. (Bug #23049170)

* Important Change: When started with the --initialize
(http://dev.mysql.com/doc/refman/5.7/en/server-options.ht
ml#option_mysqld_initialize
<http://dev.mysql.com/doc/refman/5.7/en/server-options.html#option_mysqld_initialize>)
option, mysqld no longer
enables the NDBCLUSTER
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.htm
l <http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html>) storage
engine plugin. This change was needed to
prevent attempted initialization of system databases as
distributed (rather than as specific to individual SQL
nodes), which could result in a metadata lock deadlock.
This fix also brings the behavior of --initialize in this
regard into line with that of the discontinued
--bootstrap
(http://dev.mysql.com/doc/refman/5.7/en/server-options.ht
ml#option_mysqld_bootstrap
<http://dev.mysql.com/doc/refman/5.7/en/server-options.html#option_mysqld_bootstrap>)
option, which started a
minimal mysqld instance without enabling NDB. (Bug
#22758238)

* Microsoft Windows: ndb_mgmd failed to start on 32-bit
Windows platforms, due to an issue with calling
dynamically loaded functions; such issues were also
likely to occur with other NDB programs using ndb_init().
It was found that all of the functions used are already
supported in targeted versions of Windows, so this
problem is fixed by removing the dynamic loading of these
functions and using the versions provided by the Windows
header files instead. (Bug #80876, Bug #23014820)

* Microsoft Windows: When building MySQL Cluster on Windows
using more than one parallel build job it was sometimes
possible for the build to fail because host_info.exe
could not be be installed. To fix this problem, the
install_mcc target is now always built prior to the
host_info target. (Bug #80051, Bug #22566368)

* Microsoft Windows: Performing ANALYZE TABLE
(http://dev.mysql.com/doc/refman/5.7/en/analyze-table.htm
l <http://dev.mysql.com/doc/refman/5.7/en/analyze-table.html>) on a
table having one or more indexes caused ndbmtd to
fail with an InvalidAttrInfo error due to signal
corruption. This issue occurred consistently on Windows,
but could also be encountered on other platforms. (Bug
#77716, Bug #21441297)

* Reserved send buffer for the loopback transporter,
introduced in MySQL Cluster NDB 7.4.8 and used by API and
management nodes for administrative signals, was
calculated incorrectly. (Bug #23093656)
References: This issue is a regression of: Bug #21664515.

* During a node restart, re-creation of internal triggers
used for verifying the referential integrity of foreign
keys was not reliable, because it was possible that not
all distributed TC and LDM instances agreed on all
trigger identities. To fix this problem, an extra step is
added to the node restart sequence, during which the
trigger identities are determined by querying the current
master node. (Bug #23068914)
References: See also: Bug #23221573.

* Following the forced shutdown of one of the 2 data nodes
in a cluster where NoOfReplicas=2
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndb
d-definition.html#ndbparam-ndbd-noofreplicas
<http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndbd-definition.html#ndbparam-ndbd-noofreplicas>),
the other
data node shut down as well, due to arbitration failure.
(Bug #23006431)

* Aborting a CREATE LOGFILE GROUP
(http://dev.mysql.com/doc/refman/5.7/en/create-logfile-gr
oup.html
<http://dev.mysql.com/doc/refman/5.7/en/create-logfile-group.html>)
statement which had failed due to lack of
shared global memory was not performed correctly, causing
node failure. In addition, the transaction in which this
occurred was not rolled back correctly, also causing any
subsequent CREATE LOGFILE GROUP to fail. (Bug #22982618)

* The ndbinfo.tc_time_track_stats
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndb
info-tc-time-track-stats.html
<http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndbinfo-tc-time-track-stats.html>)
table uses histogram
buckets to give a sense of the distribution of latencies.
The sizes of these bucket were also reported as HISTOGRAM
BOUNDARY INFO messages during data node startup; this
printout was redundant and so has been removed. (Bug
#22819868)

* Online upgrades from previous versions of MySQL Cluster
to MySQL Cluster NDB 7.5 were not possible due to missing
entries in the matrix used to test upgrade compatibility
between versions. (Bug #22024947)

* A failure occurred in DBTUP in debug builds when
variable-sized pages for a fragment totalled more than 4
GB. (Bug #21313546)

* Restoration of metadata with ndb_restore -m
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-pro
grams-ndb-restore.html#option_ndb_restore_restore_meta
<http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-programs-ndb-restore.html#option_ndb_restore_restore_meta>)
occasionally failed with the error message Failed to
create index... when creating a unique index. While
disgnosing this problem, it was found that the internal
error PREPARE_SEIZE_ERROR (a temporary error) was
reported as an unknown error. Now in such cases,
ndb_restore retries the creation of the unique index, and
PREPARE_SEIZE_ERROR is reported as NDB Error 748 Busy
during read of event table. (Bug #21178339)
References: See also: Bug #22989944.

* mysqld did not shut down cleanly when executing
ndb_index_stat. (Bug #21098142)

* The following improvements were made to the data node
error logging mechanism:

+ Increased the message slot size 499 bytes to 999
bytes to prevent log messages from overwriting one
another or from being truncated.

+ Added a Trace file name field to the output. This
field contains the trace file name (without any
path) and trace file number for the thread causing
the trace.

+ ndbmtd trace files are also now shown in the error
log.
(Bug #21082710)

* DBDICT and GETTABINFOREQ queue debugging were enhanced as
follows:

+ Monitoring by a data node of the progress of
GETTABINFOREQ signals can be enabled by setting
DictTrace
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluste
r-ndbd-definition.html#ndbparam-ndbd-dicttrace
<http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-ndbd-definition.html#ndbparam-ndbd-dicttrace>)
> 2.

+ Added the ApiVerbose
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluste
r-api-definition.html#ndbparam-api-apiverbose
<http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-api-definition.html#ndbparam-api-apiverbose>)
configuration parameter, which enables NDB API debug
logging for an API node where it is set greater than
or equal to 2.

+ Added DUMP code 1229 which shows the current state
of the GETTABINFOREQ queue. (See DUMP 1229
(http://dev.mysql.com/doc/ndbapi/en/ndb-internals-du
mp-command-1229.html
<http://dev.mysql.com/doc/ndbapi/en/ndb-internals-dump-command-1229.html>).)
See also The DBDICT Block
(http://dev.mysql.com/doc/ndbapi/en/ndb-internals-kernel-
blocks-dbdict.html
<http://dev.mysql.com/doc/ndbapi/en/ndb-internals-kernel-blocks-dbdict.html>).
(Bug #20368450)
References: See also: Bug #20368354.

* When a write to the ndb_binlog_index table failed during
a MySQL Server shutdown, mysqld killed the NDB binary
logging thread. (Bug #81166, Bug #23142945)

* Memory associated with table descriptions was not freed
by the internal table information method
NdbDictInterface::parseTableInfo(). (Bug #81141, Bug
#23130084)

* Fixed a memory leak that occurred when an error was
raised in ha_ndbcluster::get_metadata() or one of the
functions which this method calls. (Bug #81045, Bug
#23089566)

* An internal function used to validate connections failed
to update the connection count when creating a new Ndb
(http://dev.mysql.com/doc/ndbapi/en/ndb-ndb.html) object.
This had the potential to create a new Ndb object for
every operation validating the connection, which could
have an impact on performance, particularly when
performing schema operations. (Bug #80750, Bug #22932982)

* A table scan on an NDB
(http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.htm
l <http://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html>) table
using neither an ordered index nor any Disk Data
columns normally uses an ACC scan. If this happened while
scanning an unique but unordered index which shrank (due
to rows being deleted) after the scan started and then
grew again (rows inserted), a single row that had been
neither deleted nor inserted could be scanned twice. (Bug
#80733, Bug #22926938)

* Starting a backup in the ndb_mgm client after creating a
large number of tables caused a forced shutdown of the
cluster. (Bug #80640, Bug #228849958)

* When an SQL node was started, and joined the schema
distribution protocol, another SQL node, already waiting
for a schema change to be distributed, timed out during
that wait. This was because the code incorrectly assumed
that the new SQL node would also acknowledge the schema
distribution even though the new node joined too late to
be a participant in it.
As part of this fix, printouts of schema distribution
progress now always print the more significant part of a
bitmask before the less significant; formatting of
bitmasks in such printouts has also been improved. (Bug
#80554, Bug #22842538)

* The ndb_print_file utility failed consistently on Solaris
9 for SPARC. (Bug #80096, Bug #22579581)

* The MySQL Cluster Auto-Installer failed to work in
various ways on different platforms. (Bug #79853, Bug
#22502247)

* The internal function ndbrequire(), which, like assert(),
evaluates a given expression and terminates the process
if the expression does not evaluate as true, now includes
the failed expression in its output to the error logs.
(Bug #77021, Bug #21128318)

* Trying to drop a table during an ongoing backup failed
with the error message Unknown table; now, it fails with
Unable to alter table as backup is in progress. (Bug
#47301, Bug #11755512)
References: See also: Bug #44695, Bug #11753280.

* Disk Data: The following improvements were made to
logging during restarts by data nodes using MySQL Cluster
Disk Data:

+ The total amount of undo log to be applied by the
data node is now provided as the total number of
pages present in the log. This is a worst case
estimate.

+ Progress information is now provided at regular
intervals (once for each 30000 records) as the undo
log is applied. This information is supplied as the
number of records and number of undo log pages
applied so far during the current restart.
(Bug #22513381)

* Cluster API: Deletion of Ndb objects used a
dispoportionately high amount of CPU. (Bug #22986823)

* Cluster API: Executing a transaction with an
NdbIndexOperation
(http://dev.mysql.com/doc/ndbapi/en/ndb-ndbindexoperation
..html <http://dev.mysql.com/doc/ndbapi/en/ndb-ndbindexoperation.html>)
based on an obsolete unique index caused the data
node process to fail. Now the index is checked in such
cases, and if it cannot be used the transaction fails
with an appropriate error. (Bug #79494, Bug #22299443)

* mysql_upgrade failed to upgrade the sys schema if a sys
database directory existed but was empty. (Bug #81352,
Bug #23249846, Bug #22875519)

On behalf of the MySQL RE Team,
Lars Tangvald