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MySQL 8.0 Reference Manual  /  ...  /  Performance Schema NDB Cluster Tables

27.12.12 Performance Schema NDB Cluster Tables

Beginning with NDB 8.0.16, automatic synchronization in NDB attempts to detect and synchronize automatically all mismatches in metadata between the NDB Cluster's internal dictionary and the MySQL Server's datadictionary. This is done by default in the background at regular intervals as determined by the ndb_metadata_check_interval system variable, unless disabled using ndb_metadata_check or overridden by setting ndb_metadata_sync. Prior to NDB 8.0.21, the only information readily accessible to users about this process was in the form of logging messages and object counts available (beginning with NDB 8.0.18) as the status variables Ndb_metadata_detected_count, Ndb_metadata_synced_count, and Ndb_metadata_excluded_count (prior to NDB 8.0.22, this variable was named Ndb_metadata_blacklist_size). Beginning with NDB 8.0.21, more detailed information about the current state of automatic synchronization is exposed by a MySQL server acting as an SQL node in an NDB Cluster in these two Performance Schema tables:

  • ndb_sync_pending_objects: Displays information about NDB database objects for which mismatches have been detected between the NDB dictionary and the MySQL data dictionary. When attempting to synchronize such objects, NDB removes the object from the queue awaiting synchronization, and from this table, and tries to reconcile the mismatch. If synchronization of the object fails due to a temporary error, it is picked up and added back to the queue (and to this table) the next time NDB performs mismatch detection; if the attempts fails due a permanent error, the object is added to the ndb_sync_excluded_objects table.

  • ndb_sync_excluded_objects: Shows information about NDB database objects for which automatic synchronization has failed due to permanent errors resulting from mismatches which cannot be reconciled without manual intervention; these objects are blocklisted and not considered again for mismatch detection until this has been done.

The ndb_sync_pending_objects and ndb_sync_excluded_objects tables are present only if MySQL has support enabled for the NDBCLUSTER storage engine.

These tables are described in more detail in the following two sections.