21.3. Performance Schema Queries

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 21.2.3.2.1, "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
        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 |+-----------+-----------------+