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MySQL NDB Cluster 7.5 Release Notes  /  Changes in MySQL NDB Cluster 7.5.21 (5.7.33-ndb-7.5.21) (2021-01-19, General Availability)

Changes in MySQL NDB Cluster 7.5.21 (5.7.33-ndb-7.5.21) (2021-01-19, General Availability)

MySQL NDB Cluster 7.5.21 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 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

For an overview of changes made in MySQL NDB Cluster 7.5, see What is New in NDB Cluster 7.5.

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 5.7.33 (see Changes in MySQL 5.7.33 (2021-01-18, General Availability)).

Deprecation and Removal Notes

  • NDB Client Programs: Effective with this release, the MySQL NDB Cluster Auto-Installer ( has been has been removed from the NDB Cluster binary and source distributions, and is no longer supported. (Bug #32084831)

    References: See also: Bug #31888835.

  • ndbmemcache: ndbmemcache, which was deprecated in the previous release of NDB Cluster, has now been removed from NDB Cluster, and is no longer supported. (Bug #32106576)

Bugs Fixed

  • NDB Replication: After issuing RESET SLAVE ALL, NDB failed to detect that the replica had restarted. (Bug #31515760)

  • While retrieving sorted results from a pushed-down join using ORDER BY with the index access method (and without filesort), an SQL node sometimes unexpectedly terminated. (Bug #32203548)

  • Logging of redo log initialization showed log part indexes rather than log part numbers. (Bug #32200635)

  • Using the maximum size of an index key supported by index statistics (3056 bytes) caused buffer issues in data nodes. (Bug #32094904)

    References: See also: Bug #25038373.

  • As with writing redo log records, when the file currently used for writing global checkpoint records becomes full, writing switches to the next file. This switch is not supposed to occur until the new file is actually ready to receive the records, but no check was made to ensure that this was the case. This could lead to an unplanned data node shutdown restoring data from a backup using ndb_restore. (Bug #31585833)

  • ndb_restore encountered intermittent errors while replaying backup logs which deleted blob values; this was due to deletion of blob parts when a main table row containing blob one or more values was deleted. This is fixed by modifying ndb_restore to use the asynchronous API for blob deletes, which does not trigger blob part deletes when a blob main table row is deleted (unlike the synchronous API), so that a delete log event for the main table deletes only the row from the main table. (Bug #31546136)

  • When a table creation schema transaction is prepared, the table is in TS_CREATING state, and is changed to TS_ACTIVE state when the schema transaction commits on the DBDIH block. In the case where the node acting as DBDIH coordinator fails while the schema transaction is committing, another node starts taking over for the coordinator. The following actions are taken when handling this node failure:

    • DBDICT rolls the table creation schema transaction forward and commits, resulting in the table involved changing to TS_ACTIVE state.

    • DBDIH starts removing the failed node from tables by moving active table replicas on the failed node from a list of stored fragment replicas to another list.

    These actions are performed asynchronously many times, and when interleaving may cause a race condition. As a result, the replica list in which the replica of a failed node resides becomes nondeterministic and may differ between the recovering node (that is, the new coordinator) and other DIH participant nodes. This difference violated a requirement for knowing which list the failed node's replicas can be found during the recovery of the failed node recovery on the other participants.

    To fix this, moving active table replicas now covers not only tables in TS_ACTIVE state, but those in TS_CREATING (prepared) state as well, since the prepared schema transaction is always rolled forward.

    In addition, the state of a table creation schema transaction which is being aborted is now changed from TS_CREATING or TS_IDLE to TS_DROPPING, to avoid any race condition there. (Bug #30521812)