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 7.3.8 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/7.3/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 7.3.8 (5.6.22-ndb-7.3.8) (2015-01-21)

MySQL Cluster NDB 7.3.8 is a new release of MySQL Cluster,
based on MySQL Server 5.6 and including features from version
7.3 of the NDB storage engine, as well as fixing a number of
recently discovered bugs in previous MySQL Cluster releases.

Obtaining MySQL Cluster NDB 7.3. MySQL Cluster NDB 7.3
source code and binaries can be obtained from
http://dev.mysql.com/downloads/cluster/.

For an overview of changes made in MySQL Cluster NDB 7.3, see
MySQL Cluster Development in MySQL Cluster NDB 7.3
( http://dev.mysql.com/doc/refman/5.6/en/mysql-cluster-development-5-6-ndb-7-3.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 5.6
through MySQL 5.6.22 (see Changes in MySQL 5.6.22
(2014-12-01)
( http://dev.mysql.com/doc/relnotes/mysql/5.6/en/news-5-6-22.html )).

Functionality Added or Changed

* Performance: Recent improvements made to the
multithreaded scheduler were intended to optimize the
cache behavior of its internal data structures, with
members of these structures placed such that those local
to a given thread do not overflow into a cache line which
can be accessed by another thread. Where required, extra
padding bytes are inserted to isolate cache lines owned
(or shared) by other threads, thus avoiding invalidation
of the entire cache line if another thread writes into a
cache line not entirely owned by itself. This
optimization improved MT Scheduler performance by several
percent.
It has since been found that the optimization just
described depends on the global instance of struct
thr_repository starting at a cache line aligned base
address as well as the compiler not rearranging or adding
extra padding to the scheduler struct; it was also found
that these prerequisites were not guaranteed (or even
checked). Thus this cache line optimization has
previously worked only when g_thr_repository (that is,
the global instance) ended up being cache line aligned
only by accident. In addition, on 64-bit platforms, the
compiler added extra padding words in struct
thr_safe_pool such that attempts to pad it to a cache
line aligned size failed.
The current fix ensures that g_thr_repository is
constructed on a cache line aligned address, and the
constructors modified so as to verify cacheline aligned
adresses where these are assumed by design.
Results from internal testing show improvements in MT
Scheduler read performance of up to 10% in some cases,
following these changes. (Bug #18352514)

* Cluster API: Two new example programs, demonstrating
reads and writes of CHAR, VARCHAR, and VARBINARY column
values, have been added to storage/ndb/ndbapi-examples in
the MySQL Cluster source tree. For more information about
these programs, including source code listings, see NDB
API Simple Array Example
( http://dev.mysql.com/doc/ndbapi/en/ndbapi-examples-array-simple.html )
, and NDB API Simple Array Example Using Adapter
( http://dev.mysql.com/doc/ndbapi/en/ndbapi-examples-array-adapter.html ).

Bugs Fixed

* The global checkpoint commit and save protocols can be
delayed by various causes, including slow disk I/O. The
DIH master node monitors the progress of both of these
protocols, and can enforce a maximum lag time during
which the protocols are stalled by killing the node
responsible for the lag when it reaches this maximum.
This DIH master GCP monitor mechanism did not perform its
task more than once per master node; that is, it failed
to continue monitoring after detecting and handling a GCP
stop. (Bug #20128256)
References: See also Bug #19858151.

* When running mysql_upgrade on a MySQL Cluster SQL node,
the expected drop of the performance_schema database on
this node was instead performed on all SQL nodes
connected to the cluster. (Bug #20032861)

* A number of problems relating to the fired triggers pool
have been fixed, including the following issues:

+ When the fired triggers pool was exhausted, NDB
returned Error 218 (Out of LongMessageBuffer). A new
error code 221 is added to cover this case.

+ An additional, separate case in which Error 218 was
wrongly reported now returns the correct error.

+ Setting low values for MaxNoOfFiredTriggers led to
an error when no memory was allocated if there was
only one hash bucket.

+ An aborted transaction now releases any fired
trigger records it held. Previously, these records
were held until its ApiConnectRecord was reused by
another transaction.

+ In addition, for the Fired Triggers pool in the
internal ndbinfo.ndb$pools table, the high value
always equalled the total, due to the fact that all
records were momentarily seized when initializing
them. Now the high value shows the maximum following
completion of initialization.
(Bug #19976428)

* Online reorganization when using ndbmtd data nodes and
with binary logging by mysqld enabled could sometimes
lead to failures in the TRIX and DBLQH kernel blocks, or
in silent data corruption. (Bug #19903481)
References: See also Bug #19912988.

* The local checkpoint ScanFrag watchdog and the global
checkpoint monitor can each exclude a node when it is too
slow when participating in their respective protocols.
This exclusion was implemented by simply asking the
failing node to shut down, which in case this was delayed
(for whatever reason) could prolong the duration of the
GCP or LCP stall for other, unaffected nodes.
To minimize this time, an isolation mechanism has been
added to both protocols whereby any other live nodes
forcibly disconnect the failing node after a
predetermined amount of time. This allows the failing
node the opportunity to shut down gracefully (after
logging debugging and other information) if possible, but
limits the time that other nodes must wait for this to
occur. Now, once the remaining live nodes have processed
the disconnection of any failing nodes, they can commence
failure handling and restart the related protocol or
protocol, even if the failed node takes an excessiviely
long time to shut down. (Bug #19858151)
References: See also Bug #20128256.

* A watchdog failure resulted from a hang while freeing a
disk page in TUP_COMMITREQ, due to use of an
uninitialized block variable. (Bug #19815044, Bug #74380)

* Multiple threads crashing led to multiple sets of trace
files being printed and possibly to deadlocks. (Bug
#19724313)

* When a client retried against a new master a schema
transaction that failed previously against the previous
master while the latter was restarting, the lock obtained
by this transaction on the new master prevented the
previous master from progressing past start phase 3 until
the client was terminated, and resources held by it were
cleaned up. (Bug #19712569, Bug #74154)

* When using the NDB storage engine, the maximum possible
length of a database or table name is 63 characters, but
this limit was not always strictly enforced. This meant
that a statement using a name having 64 characters such
CREATE DATABASE, DROP DATABASE, or ALTER TABLE RENAME
could cause the SQL node on which it was executed to
fail. Now such statements fail with an appropriate error
message. (Bug #19550973)

* When a new data node started, API nodes were allowed to
attempt to register themselves with the data node for
executing transactions before the data node was ready.
This forced the API node to wait an extra heartbeat
interval before trying again.
To address this issue, a number of HA_ERR_NO_CONNECTION
errors (Error 4009) that could be issued during this time
have been changed to Cluster temporarily unavailable
errors (Error 4035), which should allow API nodes to use
new data nodes more quickly than before. As part of this
fix, some errors which were incorrectly categorised have
been moved into the correct categories, and some errors
which are no longer used have been removed. (Bug
#19524096, Bug #73758)

* When executing very large pushdown joins involving one or
more indexes each defined over several columns, it was
possible in some cases for the DBSPJ block (see The DBSPJ
Block
( http://dev.mysql.com/doc/ndbapi/en/ndb-internals-kernel-blocks-dbspj.html ))
in the NDB kernel to generate SCAN_FRAGREQ signals that were
excessively large. This caused data nodes to fail when these
could not be handled correctly, due to a hard limit in the
kernel on the size of such signals (32K). This fix bypasses
that limitation by breaking up SCAN_FRAGREQ data that is too
large for one such signal, and sending the SCAN_FRAGREQ as a
chunked or fragmented signal instead. (Bug #19390895)

* ndb_index_stat sometimes failed when used against a table
containing unique indexes. (Bug #18715165)

* Queries against tables containing a CHAR(0) columns
failed with ERROR 1296 (HY000): Got error 4547
'RecordSpecification has overlapping offsets' from
NDBCLUSTER. (Bug #14798022)

* In the NDB kernel, it was possible for a
TransporterFacade object to reset a buffer while the data
contained by the buffer was being sent, which could lead
to a race condition. (Bug #75041, Bug #20112981)

* mysql_upgrade failed to drop and recreate the ndbinfo
database and its tables as expected. (Bug #74863, Bug
#20031425)

* Due to a lack of memory barriers, MySQL Cluster programs
such as ndbmtd did not compile on POWER platforms. (Bug
#74782, Bug #20007248)

* In some cases, when run against a table having an AFTER
DELETE trigger, a DELETE statement that matched no rows
still caused the trigger to execute. (Bug #74751, Bug
#19992856)

* A basic requirement of the NDB storage engine's design is
that the transporter registry not attempt to receive data
(TransporterRegistry::performReceive()) from and update
the connection status
(TransporterRegistry::update_connections()) of the same
set of transporters concurrently, due to the fact that
the updates perform final cleanup and reinitialization of
buffers used when receiving data. Changing the contents
of these buffers while reading or writing to them could
lead to "garbage" or inconsistent signals being read or
written.
During the course of work done previously to improve the
implementation of the transporter facade, a mutex
intended to protect against the concurrent use of the
performReceive() and update_connections()) methods on the
same transporter was inadvertently removed. This fix adds
a watchdog check for concurrent usage. In addition,
update_connections() and performReceive() calls are now
serialized together while polling the transporters. (Bug
#74011, Bug #19661543)

* ndb_restore failed while restoring a table which
contained both a built-in conversion on the primary key
and a staging conversion on a TEXT column.
During staging, a BLOB table is created with a primary
key column of the target type. However, a conversion
function was not provided to convert the primary key
values before loading them into the staging blob table,
which resulted in corrupted primary key values in the
staging BLOB table. While moving data from the staging
table to the target table, the BLOB read failed because
it could not find the primary key in the BLOB table.
Now all BLOB tables are checked to see whether there are
conversions on primary keys of their main tables. This
check is done after all the main tables are processed, so
that conversion functions and parameters have already
been set for the main tables. Any conversion functions
and parameters used for the primary key in the main table
are now duplicated in the BLOB table. (Bug #73966, Bug
#19642978)

* Corrupted messages to data nodes sometimes went
undetected, causing a bad signal to be delivered to a
block which aborted the data node. This failure in
combination with disconnecting nodes could in turn cause
the entire cluster to shut down.
To keep this from happening, additional checks are now
made when unpacking signals received over TCP, including
checks for byte order, compression flag (which must not
be used), and the length of the next message in the
receive buffer (if there is one).
Whenever two consecutive unpacked messages fail the
checks just described, the current message is assumed to
be corrupted. In this case, the transporter is marked as
having bad data and no more unpacking of messages occurs
until the transporter is reconnected. In addition, an
entry is written to the cluster log containing the error
as well as a hex dump of the corrupted message. (Bug
#73843, Bug #19582925)

* Transporter send buffers were not updated properly
following a failed send. (Bug #45043, Bug #20113145)

* ndb_restore --print_data truncated TEXT and BLOB column
values to 240 bytes rather than 256 bytes.

* Disk Data: When a node acting as a DICT master fails, the
arbitrator selects another node to take over in place of
the failed node. During the takeover procedure, which
includes cleaning up any schema transactions which are
still open when the master failed, the disposition of the
uncommitted schema transaction is decided. Normally this
transaction be rolled back, but if it has completed a
sufficient portion of a commit request, the new master
finishes processing the commit. Until the fate of the
transaction has been decided, no new TRANS_END_REQ
messages from clients can be processed. In addition,
since multiple concurrent schema transactions are not
supported, takeover cleanup must be completed before any
new transactions can be started.
A similar restriction applies to any schema operations
which are performed in the scope of an open schema
transaction. The counter used to coordinate schema
operation across all nodes is employed both during
takeover processing and when executing any non-local
schema operations. This means that starting a schema
operation while its schema transaction is in the takeover
phase causes this counter to be overwritten by concurrent
uses, with unpredictable results.
The scenarios just described were handled previously
using a pseudo-random delay when recovering from a node
failure. Now we check before the new master has rolled
forward or backwards any schema transactions remaining
after the failure of the previous master and avoid
starting new schema transactions or performing operations
using old transactions until takeover processing has
cleaned up after the abandoned transaction. (Bug
#19874809, Bug #74503)

* Disk Data: When a node acting as DICT master fails, it is
still possible to request that any open schema
transaction be either committed or aborted by sending
this request to the new DICT master. In this event, the
new master takes over the schema transaction and reports
back on whether the commit or abort request succeeded. In
certain cases, it was possible for the new master to be
misidentified---that is, the request was sent to the
wrong node, which responded with an error that was
interpreted by the client application as an aborted
schema transaction, even in cases where the transaction
could have been successfully committed, had the correct
node been contacted. (Bug #74521, Bug #19880747)

* Cluster Replication: When an NDB client thread made a
request to flush the binary log using statements such as
FLUSH BINARY LOGS or SHOW BINLOG EVENTS, this caused not
only the most recent changes made by this client to be
flushed, but all recent changes made by all other clients
to be flushed as well, even though this was not needed.
This behavior caused unnecessary waiting for the
statement to execute, which could lead to timeouts and
other issues with replication. Now such statements flush
the most recent database changes made by the requesting
thread only.
As part of this fix, the status variables
Ndb_last_commit_epoch_server,
Ndb_last_commit_epoch_session, and
Ndb_slave_max_replicated_epoch, originally implemented in
MySQL Cluster NDB 7.4, are also now available in MySQL
Cluster NDB 7.3. For descriptions of these variables, see
MySQL Cluster Status Variables
( http://dev.mysql.com/doc/refman/5.6/en/mysql-cluster-status-variables.html ).
For further information, see MySQL Cluster Replication Conflict
Resolution
( http://dev.mysql.com/doc/refman/5.6/en/mysql-cluster-replication-conflict-resolution.html ).
(Bug #19793475)

* Cluster Replication: It was possible using wildcards to
set up conflict resolution for an exceptions table (that
is, a table named using the suffix $EX), which should not
be allowed. Now when a replication conflict function is
defined using wildcard expressions, these are checked for
possible matches so that, in the event that the function
would cover an exceptions table, it is not set up for
this table. (Bug #19267720)

* Cluster API: It was possible to delete an
Ndb_cluster_connection object while there remained
instances of Ndb using references to it. Now the
Ndb_cluster_connection destructor waits for all related
Ndb objects to be released before completing. (Bug
#19999242)
References: See also Bug #19846392.

* Cluster API: The buffer allocated by an NdbScanOperation
for receiving scanned rows was not released until the
NdbTransaction owning the scan operation was closed. This
could lead to excessive memory usage in an application
where multiple scans were created within the same
transaction, even if these scans were closed at the end
of their lifecycle, unless NdbScanOperation::close() was
invoked with the releaseOp argument equal to true. Now
the buffer is released whenever the cursor navigating the
result set is closed with NdbScanOperation::close(),
regardless of the value of this argument. (Bug #75128,
Bug #20166585)

* ClusterJ: The following errors were logged at the SEVERE
level; they are now logged at the NORMAL level, as they
should be:

+ Duplicate primary key

+ Duplicate unique key

+ Foreign key constraint error: key does not exist

+ Foreign key constraint error: key exists
(Bug #20045455)

* ClusterJ: The com.mysql.clusterj.tie class gave off a
logging message at the INFO logging level for every
single query, which was unnecessary and was affecting the
performance of applications that used ClusterJ. (Bug
#20017292)

* ClusterJ: ClusterJ reported a segmentation violation when
an application closed a session factory while some
sessions were still active. This was because MySQL
Cluster allowed an Ndb_cluster_connection object be to
deleted while some Ndb instances were still active, which
might result in the usage of null pointers by ClusterJ.
This fix stops that happening by preventing ClusterJ from
closing a session factory when any of its sessions are
still active. (Bug #19846392)
References: See also Bug #19999242.

On Behalf of the MySQL Cluster and the Oracle/MySQL RE Team

- Bjorn Munch

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