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The Performance Schema maintains statement event summary tables that contain information about minimum, maximum, and average statement latency (seeSection 29.12.20.3, “Statement Summary Tables”). Those tables permit high-level assessment of system performance. To permit assessment at a more fine-grained level, the Performance Schema also collects histogram data for statement latencies. These histograms provide additional insight into latency distributions.

Section 29.12.6, “Performance Schema Statement Event Tables” describes the events on which statement summaries are based. See that discussion for information about the content of statement events, the current and historical statement event tables, and how to control statement event collection, which is partially disabled by default.

Example statement histogram information:

mysql> SELECT *       FROM performance_schema.events_statements_histogram_by_digest       WHERE SCHEMA_NAME = 'mydb' AND DIGEST = 'bb3f69453119b2d7b3ae40673a9d4c7c'       AND COUNT_BUCKET > 0 ORDER BY BUCKET_NUMBER\G*************************** 1. row ***************************           SCHEMA_NAME: mydb                DIGEST: bb3f69453119b2d7b3ae40673a9d4c7c         BUCKET_NUMBER: 42      BUCKET_TIMER_LOW: 66069344     BUCKET_TIMER_HIGH: 69183097          COUNT_BUCKET: 1COUNT_BUCKET_AND_LOWER: 1       BUCKET_QUANTILE: 0.058824*************************** 2. row ***************************           SCHEMA_NAME: mydb                DIGEST: bb3f69453119b2d7b3ae40673a9d4c7c         BUCKET_NUMBER: 43      BUCKET_TIMER_LOW: 69183097     BUCKET_TIMER_HIGH: 72443596          COUNT_BUCKET: 1COUNT_BUCKET_AND_LOWER: 2       BUCKET_QUANTILE: 0.117647*************************** 3. row ***************************           SCHEMA_NAME: mydb                DIGEST: bb3f69453119b2d7b3ae40673a9d4c7c         BUCKET_NUMBER: 44      BUCKET_TIMER_LOW: 72443596     BUCKET_TIMER_HIGH: 75857757          COUNT_BUCKET: 2COUNT_BUCKET_AND_LOWER: 4       BUCKET_QUANTILE: 0.235294*************************** 4. row ***************************           SCHEMA_NAME: mydb                DIGEST: bb3f69453119b2d7b3ae40673a9d4c7c         BUCKET_NUMBER: 45      BUCKET_TIMER_LOW: 75857757     BUCKET_TIMER_HIGH: 79432823          COUNT_BUCKET: 6COUNT_BUCKET_AND_LOWER: 10       BUCKET_QUANTILE: 0.625000...

For example, in row 3, these values indicate that 23.52% of queries run in under 75.86 microseconds:

BUCKET_TIMER_HIGH: 75857757  BUCKET_QUANTILE: 0.235294

In row 4, these values indicate that 62.50% of queries run in under 79.44 microseconds:

BUCKET_TIMER_HIGH: 79432823  BUCKET_QUANTILE: 0.625000

Each statement histogram summary table has one or more grouping columns to indicate how the table aggregates events:

A histogram consists ofN buckets, where each row represents one bucket, with the bucket number indicated by theBUCKET_NUMBER column. Bucket numbers begin with 0.

Each statement histogram summary table has these summary columns containing aggregated values:

The statement histogram summary tables have these indexes:

TRUNCATE TABLE is permitted for statement histogram summary tables. Truncation sets theCOUNT_BUCKET andCOUNT_BUCKET_AND_LOWER columns to 0.

In addition, truncatingevents_statements_summary_by_digest implicitly truncatesevents_statements_histogram_by_digest, and truncatingevents_statements_summary_global_by_event_name implicitly truncatesevents_statements_histogram_global.