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:
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.
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