The Ultimate Guide to High Availability with MariaDB

Performance Schema events_statements_summary_by_digest Table

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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:

ColumnDescription
SCHEMA NAMEDatabase name. Records are summarised together with DIGEST.
DIGESTPerformance Schema digest. Records are summarised together with SCHEMA NAME.
DIGEST TEXTThe unhashed form of the digest.
COUNT_STARNumber of summarized events
SUM_TIMER_WAITTotal wait time of the summarized events that are timed.
MIN_TIMER_WAITMinimum wait time of the summarized events that are timed.
AVG_TIMER_WAITAverage wait time of the summarized events that are timed.
MAX_TIMER_WAITMaximum wait time of the summarized events that are timed.
SUM_LOCK_TIMESum of the LOCK_TIME column in the events_statements_current table.
SUM_ERRORSSum of the ERRORS column in the events_statements_current table.
SUM_WARNINGSSum of the WARNINGS column in the events_statements_current table.
SUM_ROWS_AFFECTEDSum of the ROWS_AFFECTED column in the events_statements_current table.
SUM_ROWS_SENTSum of the ROWS_SENT column in the events_statements_current table.
SUM_ROWS_EXAMINEDSum of the ROWS_EXAMINED column in the events_statements_current table.
SUM_CREATED_TMP_DISK_TABLESSum of the CREATED_TMP_DISK_TABLES column in the events_statements_current table.
SUM_CREATED_TMP_TABLESSum of the CREATED_TMP_TABLES column in the events_statements_current table.
SUM_SELECT_FULL_JOINSum of the SELECT_FULL_JOIN column in the events_statements_current table.
SUM_SELECT_FULL_RANGE_JOINSum of the SELECT_FULL_RANGE_JOIN column in the events_statements_current table.
SUM_SELECT_RANGESum of the SELECT_RANGE column in the events_statements_current table.
SUM_SELECT_RANGE_CHECKSum of the SELECT_RANGE_CHECK column in the events_statements_current table.
SUM_SELECT_SCANSum of the SELECT_SCAN column in the events_statements_current table.
SUM_SORT_MERGE_PASSESSum of the SORT_MERGE_PASSES column in the events_statements_current table.
SUM_SORT_RANGESum of the SORT_RANGE column in the events_statements_current table.
SUM_SORT_ROWSSum of the SORT_ROWS column in the events_statements_current table.
SUM_SORT_SCANSum of the SORT_SCAN column in the events_statements_current table.
SUM_NO_INDEX_USEDSum of the NO_INDEX_USED column in the events_statements_current table.
SUM_NO_GOOD_INDEX_USEDSum of the NO_GOOD_INDEX_USED column in the events_statements_current table.
FIRST_SEENTime at which the digest was first seen.
LAST_SEENTime 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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