Performance Schema events_statements_summary_by_digest Table
The Performance Schema digest is a hashed, normalized form of a statement with the specific data values removed. It allows statistics to be gathered for similar kinds of statements.
The Performance Schema events_statements_summary_by_digest table records statement events summarized by schema and digest. It contains the following columns:
| Column | Description |
|---|---|
SCHEMA NAME | Database name. Records are summarised together with DIGEST. |
DIGEST | Performance Schema digest. Records are summarised together with SCHEMA NAME. |
DIGEST TEXT | The unhashed form of the digest. |
COUNT_STAR | Number of summarized events |
SUM_TIMER_WAIT | Total wait time of the summarized events that are timed. |
MIN_TIMER_WAIT | Minimum wait time of the summarized events that are timed. |
AVG_TIMER_WAIT | Average wait time of the summarized events that are timed. |
MAX_TIMER_WAIT | Maximum wait time of the summarized events that are timed. |
SUM_LOCK_TIME | Sum of the LOCK_TIME column in the events_statements_current table. |
SUM_ERRORS | Sum of the ERRORS column in the events_statements_current table. |
SUM_WARNINGS | Sum of the WARNINGS column in the events_statements_current table. |
SUM_ROWS_AFFECTED | Sum of the ROWS_AFFECTED column in the events_statements_current table. |
SUM_ROWS_SENT | Sum of the ROWS_SENT column in the events_statements_current table. |
SUM_ROWS_EXAMINED | Sum of the ROWS_EXAMINED column in the events_statements_current table. |
SUM_CREATED_TMP_DISK_TABLES | Sum of the CREATED_TMP_DISK_TABLES column in the events_statements_current table. |
SUM_CREATED_TMP_TABLES | Sum of the CREATED_TMP_TABLES column in the events_statements_current table. |
SUM_SELECT_FULL_JOIN | Sum of the SELECT_FULL_JOIN column in the events_statements_current table. |
SUM_SELECT_FULL_RANGE_JOIN | Sum of the SELECT_FULL_RANGE_JOIN column in the events_statements_current table. |
SUM_SELECT_RANGE | Sum of the SELECT_RANGE column in the events_statements_current table. |
SUM_SELECT_RANGE_CHECK | Sum of the SELECT_RANGE_CHECK column in the events_statements_current table. |
SUM_SELECT_SCAN | Sum of the SELECT_SCAN column in the events_statements_current table. |
SUM_SORT_MERGE_PASSES | Sum of the SORT_MERGE_PASSES column in the events_statements_current table. |
SUM_SORT_RANGE | Sum of the SORT_RANGE column in the events_statements_current table. |
SUM_SORT_ROWS | Sum of the SORT_ROWS column in the events_statements_current table. |
SUM_SORT_SCAN | Sum of the SORT_SCAN column in the events_statements_current table. |
SUM_NO_INDEX_USED | Sum of the NO_INDEX_USED column in the events_statements_current table. |
SUM_NO_GOOD_INDEX_USED | Sum of the NO_GOOD_INDEX_USED column in the events_statements_current table. |
FIRST_SEEN | Time at which the digest was first seen. |
LAST_SEEN | Time at which the digest was most recently seen. |
The *_TIMER_WAIT columns only calculate results for timed events, as non-timed events have a NULL wait time.
The events_statements_summary_by_digest table is limited in size by the performance_schema_digests_size system variable. Once the limit has been reached and the table is full, all entries are aggregated in a row with a NULL digest. The COUNT_STAR value of this NULL row indicates how many digests are recorded in the row and therefore gives an indication of whether performance_schema_digests_size should be increased to provide more accurate statistics.
