Lars Tangvald MySQL Cluster 7.4.9 has been released
Jan 18, 2016; 23:28
MySQL Cluster 7.4.9 has been released
Dear MySQL Users,
MySQL Cluster is the distributed, shared-nothing variant of MySQL. This storage engine provides:
MySQL Cluster 7.4 makes significant advances in performance; operational efficiency (such as enhanced reporting and faster restarts and upgrades) and conflict detection and resolution for active-active replication between MySQL Clusters.
MySQL Cluster 7.4.9, has been released and can be downloaded from
where you will also find Quick Start guides to help you get your first MySQL Cluster database up and running.
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
Changes in MySQL Cluster NDB 7.4.9 (5.6.28-ndb-7.4.9) (2016-01-18 )
MySQL Cluster NDB 7.4.9 is a new release of MySQL Cluster 7.4, based on MySQL Server 5.6 and including features in version 7.4 of the NDB storage engine, as well as fixing recently discovered bugs in previous MySQL Cluster releases.
Obtaining MySQL Cluster NDB 7.4. MySQL Cluster NDB 7.4 source code and binaries can be obtained from http://dev.mysql.com/downloads/cluster/.
For an overview of changes made in MySQL Cluster NDB 7.4, see MySQL Cluster Development in MySQL Cluster NDB 7.4 ( http://dev.mysql.com/doc/refman/5.6/en/mysql-cluster-development- 5-6-ndb-7-4.htm l).
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 5.6.28 (see Changes in MySQL 5.6.28 (2015-12-07) (http://dev.mysql.com/doc/relnotes/mysql/5.6/en/news-5-6-28.html)).
Functionality Added or Changed
* Important Change: Previously, the NDB scheduler always optimized for speed against throughput in a predetermined manner (this was hard coded); this balance can now be set using the SchedulerResponsiveness data node configuration parameter. This parameter accepts an integer in the range of 0-10 inclusive, with 5 as the default. Higher values provide better response times relative to throughput. Lower values provide increased throughput, but impose longer response times. (Bug #78531, Bug #21889312)
* Added the tc_time_track_stats table to the ndbinfo information database. This table provides time-tracking information relating to transactions, key operations, and scan operations performed by NDB. (Bug #78533, Bug #21889652)
* Cluster Replication: Normally, RESET SLAVE causes all entries to be deleted from the mysql.ndb_apply_status table. This release adds the ndb_clear_apply_status system variable, which makes it possible to override this behavior. This variable is ON by default; setting it to OFF keeps RESET SLAVE from purging the ndb_apply_status table. (Bug #12630403)
* Important Change: Users can now set the number and length of connection timeouts allowed by most NDB programs with the --connect-retries and --connect-retry-delay command line options introduced for the programs in this release. For ndb_mgm, --connect-retries supersedes the existing --try-reconnect option. (Bug #57576, Bug #11764714)
* When executing a schema operation such as CREATE TABLE on a MySQL Cluster with multiple SQL nodes, it was possible for the SQL node on which the operation was performed to time out while waiting for an acknowledgement from the others. This could occur when different SQL nodes had different settings for --ndb-log-updated-only, --ndb-log-update-as-write, or other mysqld options effecting binary logging by NDB. This happened due to the fact that, in order to distribute schema changes between them, all SQL nodes subscribe to changes in the ndb_schema system table, and that all SQL nodes are made aware of each others subscriptions by subscribing to TE_SUBSCRIBE and TE_UNSUBSCRIBE events. The names of events to subscribe to are constructed from the table names, adding REPL$ or REPLF$ as a prefix. REPLF$ is used when full binary logging is specified for the table. The issue described previously arose because different values for the options mentioned could lead to different events being subscribed to by different SQL nodes, meaning that all SQL nodes were not necessarily aware of each other, so that the code that handled waiting for schema distribution to complete did not work as designed. To fix this issue, MySQL Cluster now treats the ndb_schema table as a special case and enforces full binary logging at all times for this table, independent of any settings for mysqld binary logging options. (Bug #22174287, Bug #79188)
* Attempting to create an NDB table having greater than the maximum supported combined width for all BIT columns (4096) caused data node failure when these columns were defined with COLUMN_FORMAT DYNAMIC. (Bug #21889267)
* Creating a table with the maxmimum supported number of columns (512) all using COLUMN_FORMAT DYNAMIC led to data node failures. (Bug #21863798)
* In certain cases, a cluster failure (error 4009) was reported as Unknown error code. (Bug #21837074)
* For a timeout in GET_TABINFOREQ while executing a CREATE INDEX statement, mysqld returned Error 4243 (Index not found) instead of the expected Error 4008 (Receive from NDB failed). The fix for this bug also fixes similar timeout issues for a number of other signals that are sent the DBDICT kernel block as part of DDL operations, including ALTER_TAB_REQ, CREATE_INDX_REQ, DROP_FK_REQ, DROP_INDX_REQ, INDEX_STAT_REQ, DROP_FILE_REQ, CREATE_FILEGROUP_REQ, DROP_FILEGROUP_REQ, CREATE_EVENT, WAIT_GCP_REQ, DROP_TAB_REQ, and LIST_TABLES_REQ, as well as several internal functions used in handling NDB schema operations. (Bug #21277472) References: See also Bug #20617891, Bug #20368354, Bug #19821115.
* Using ndb_mgm STOP -f to force a node shutdown even when it triggered a complete shutdown of the cluster, it was possible to lose data when a sufficient number of nodes were shut down, triggering a cluster shutodwn, and the timing was such that SUMA handovers had been made to nodes already in the process of shutting down. (Bug #17772138)
* The internal NdbEventBuffer::set_total_buckets() method calculated the number of remaining buckets incorrectly. This caused any incomplete epoch to be prematurely completed when the SUB_START_CONF signal arrived out of order. Any events belonging to this epoch arriving later were then ignored, and so effectively lost, which resulted in schema changes not being distributed correctly among SQL nodes. (Bug #79635, Bug #22363510)
* Compilation of MySQL Cluster failed on SUSE Linux Enterprise Server 12. (Bug #79429, Bug #22292329)
* Schema events were appended to the binary log out of order relative to non-schema events. This was caused by the fact that the binlog injector did not properly handle the case where schema events and non-schema events were from different epochs. This fix modifies the handling of events from the two schema and non-schema event streams such that events are now always handled one epoch at a time, starting with events from the oldest available epoch, without regard to the event stream in which they occur. (Bug #79077, Bug #22135584, Bug #20456664)
* When executed on an NDB table, ALTER TABLE ... DROP INDEX made changes to an internal array referencing the indexes before the index was actually dropped, and did not revert these changes in the event that the drop was not completed. One effect of this was that, after attempting to drop an index on which there was a foreign key dependency, the expected error referred to the wrong index, and subsequent attempts using SQL to modify indexes of this table failed. (Bug #78980, Bug #22104597)
* NDB failed during a node restart due to the status of the current local checkpoint being set but not as active, even though it could have other states under such conditions. (Bug #78780, Bug #21973758)
* ndbmtd checked for signals being sent only after a full cycle in run_job_buffers, which is performed for all job buffer inputs. Now this is done as part of run_job_buffers itself, avoiding executing for extended periods without sending to other nodes or flushing signals to other threads. (Bug #78530, Bug #21889088)
* In MySQL Cluster 7.4 scan executions was optimised by handling multiple rows at a time. This has two effects, 1) it gives scans higher prio compared to key lookup operations, 2) it changes the behaviour of the scheduler. 2) was fixed, restoring the former scheduling behaviour. 1) is kept since it has a significant performance benefit but means were provided for change of this in exceptional circumstances. (Bug #78526, Bug #21886644)
* Disk Data: A unique index on a column of an NDB table is implemented with an associated internal ordered index, used for scanning. While dropping an index, this ordered index was dropped first, followed by the drop of the unique index itself. This meant that, when the drop was rejected due to (for example) a constraint violation, the statement was rejected but the associated ordered index remained deleted, so that any subsequent operation using a scan on this table failed. We fix this problem by causing the unique index to be removed first, before removing the ordered index; removal of the related ordered index is no longer performed when removal of a unique index fails. (Bug #78306, Bug #21777589)
* Cluster Replication: While the binary log injector thread was handling failure events, it was possible for all NDB tables to be left indefinitely in read-only mode. This was due to a race condition between the binlog injector thread and the utility thread handling events on the ndb_schema table, and to the fact that, when handling failure events, the binlog injector thread places all NDB tables in read-only mode until all such events are handled and the thread restarts itself. When the binlog inject thread receives a group of one or more failure events, it drops all other existing event operations and expects no more events from the utility thread until it has handled all of the failure events and then restarted itself. However, it was possible for the utility thread to continue attempting binary log setup while the injector thread was handling failures and thus attempting to create the schema distribution tables as well as event subscriptions on these tables. If the creation of these tables and event subscriptions occurred during this time, the binlog injector thread's expectation that there were no further event operations was never met; thus, the injector thread never restarted, and NDB tables remained in read-only as described previously. To fix this problem, the Ndb object that handles schema events is now definitely dropped once the ndb_schema table drop event is handled, so that the utility thread cannot create any new events until after the injector thread has restarted, at which time, a new Ndb object for handling schema events is created. (Bug #17674771, Bug #19537961, Bug #22204186, Bug #22361695)
* Cluster API: The binlog injector did not work correctly with TE_INCONSISTENT event type handling by Ndb::nextEvent(). (Bug #22135541) References: See also Bug #20646496.
* Cluster API: Ndb::pollEvents() and pollEvents2() were slow to receive events, being dependent on other client threads or blocks to perform polling of transporters on their behalf. This fix allows a client thread to perform its own transporter polling when it has to wait in either of these methods. Introduction of transporter polling also revealed a problem with missing mutex protection in the ndbcluster_binlog handler, which has been added as part of this fix. (Bug #20957068, Bug #22224571, Bug #79311)
* Cluster API: Garbage collection is performed on several objects in the implementation of NdbEventOperation, based on which GCIs have been consumed by clients, including those that have been dropped by Ndb::dropEventOperation(). In this implementation, the assumption was made that the global checkpoint index (GCI) is always monotonically increasing, although this is not the case during an initial restart, when the GCI is reset. This could lead to event objects in the NDB API being released prematurely or not at all, in the latter case causing a resource leak. To prevent this from happening, the NDB event object's implementation now tracks, internally, both the GCI and the generation of the GCI; the generation is incremented whenever the node process is restarted, and this value is now used to provide a monotonically increasing sequence. (Bug #73781, Bug #21809959)
On behalf of the MySQL Release Team, Lars Tangvald
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