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 *note performance-schema-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 |
+-----------+-----------------+File: manual.info.tmp, Node: performance-schema-instrument-naming, Next: performance-schema-status-monitoring, Prev: performance-schema-queries, Up: performance-schema