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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 appropriateWHERE clauses that restrict what event information to select from the events available after pre-filtering has been applied.

InSection 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 aWHERE 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 |+-----------+-----------------+