MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
Pre-filtering limits which event information is collected and is
independent of any particular user. By contrast, post-filtering is
performed by individual users through the use of queries with
appropriate WHERE
clauses that restrict what
event information to select from the events available after
pre-filtering has been applied.
In Section 25.4.3, “Event Pre-Filtering”, an example
showed how to pre-filter for file instruments. If the event tables
contain both file and nonfile information, post-filtering is
another way to see information only for file events. Add a
WHERE
clause to queries to restrict event
selection appropriately:
mysql>SELECT THREAD_ID, NUMBER_OF_BYTES
FROM performance_schema.events_waits_history
WHERE EVENT_NAME LIKE 'wait/io/file/%'
AND NUMBER_OF_BYTES IS NOT NULL;
+-----------+-----------------+ | THREAD_ID | NUMBER_OF_BYTES | +-----------+-----------------+ | 11 | 66 | | 11 | 47 | | 11 | 139 | | 5 | 24 | | 5 | 834 | +-----------+-----------------+