MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6

21.5.7.3 Event Buffer Reporting in the Cluster Log

NDB uses one or more memory buffers for events received from the data nodes. There is one such buffer for each Ndb object subscribing to table events, which means that there are usually two buffers for each mysqld performing binary logging (one buffer for schema events, and one for data events). Each buffer contains epochs made up of events. These events consist of operation types (insert, update, delete) and row data (before and after images plus metadata).

NDB generates messages in the cluster log to describe the state of these buffers. Although these reports appear in the cluster log, they refer to buffers on API nodes (unlike most other cluster log messages, which are generated by data nodes). These messages and the data structures underlying them were changed significantly in NDB 7.5.1, with the addition of the NDB_LE_EventBufferStatus2 event type and the ndb_logevent_EventBufferStatus2 data structure (see The Ndb_logevent_type Type). The remainder of this discussion focuses on the implementation based on NDB_LE_EventBufferStatus2.

Event buffer logging reports in the cluster log use the format shown here:

Node node_id: Event buffer status (object_id):
used=bytes_used (percent_used% of alloc)
alloc=bytes_allocated (percent_alloc% of max) max=bytes_available
latest_consumed_epoch=latest_consumed_epoch
latest_buffered_epoch=latest_buffered_epoch
report_reason=report_reason

The fields making up this report are listed here, with descriptions:

The latest_consumed_epoch and latest_buffered_epoch fields correspond, respectively, to the apply_gci and latest_gci fields of the old-style event buffer logging messages used prior to NDB 7.5.1.

Possible reasons for reporting are described in the following list: