Performance Schema Queries-opracowanie

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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 |
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