27.12.18.8 Table I/O and Lock Wait Summary Tables

The following sections describe the table I/O and lock wait summary tables:

table_io_waits_summary_by_index_usage: Table I/O waits per index
table_io_waits_summary_by_table: Table I/O waits per table
table_lock_waits_summary_by_table: Table lock waits per table

27.12.18.8.1 The table_io_waits_summary_by_table Table

The table_io_waits_summary_by_table table aggregates all table I/O wait events, as generated by the wait/io/table/sql/handler instrument. The grouping is by table.

The table_io_waits_summary_by_table table has these grouping columns to indicate how the table aggregates events: OBJECT_TYPE, OBJECT_SCHEMA, and OBJECT_NAME. These columns have the same meaning as in the events_waits_current table. They identify the table to which the row applies.

table_io_waits_summary_by_table has the following summary columns containing aggregated values. As indicated in the column descriptions, some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. For example, columns that aggregate all writes hold the sum of the corresponding columns that aggregate inserts, updates, and deletes. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.

COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT
These columns aggregate all I/O operations. They are the same as the sum of the corresponding xxx_READ and xxx_WRITE columns.
COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ
These columns aggregate all read operations. They are the same as the sum of the corresponding xxx_FETCH columns.
COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE
These columns aggregate all write operations. They are the same as the sum of the corresponding xxx_INSERT, xxx_UPDATE, and xxx_DELETE columns.
COUNT_FETCH, SUM_TIMER_FETCH, MIN_TIMER_FETCH, AVG_TIMER_FETCH, MAX_TIMER_FETCH
These columns aggregate all fetch operations.
COUNT_INSERT, SUM_TIMER_INSERT, MIN_TIMER_INSERT, AVG_TIMER_INSERT, MAX_TIMER_INSERT
These columns aggregate all insert operations.
COUNT_UPDATE, SUM_TIMER_UPDATE, MIN_TIMER_UPDATE, AVG_TIMER_UPDATE, MAX_TIMER_UPDATE
These columns aggregate all update operations.
COUNT_DELETE, SUM_TIMER_DELETE, MIN_TIMER_DELETE, AVG_TIMER_DELETE, MAX_TIMER_DELETE
These columns aggregate all delete operations.

The table_io_waits_summary_by_table table has these indexes:

Unique index on (OBJECT_TYPE, OBJECT_SCHEMA, OBJECT_NAME)

TRUNCATE TABLE is permitted for table I/O summary tables. It resets the summary columns to zero rather than removing rows. Truncating this table also truncates the table_io_waits_summary_by_index_usage table.

27.12.18.8.2 The table_io_waits_summary_by_index_usage Table

The table_io_waits_summary_by_index_usage table aggregates all table index I/O wait events, as generated by the wait/io/table/sql/handler instrument. The grouping is by table index.

The columns of table_io_waits_summary_by_index_usage are nearly identical to table_io_waits_summary_by_table. The only difference is the additional group column, INDEX_NAME, which corresponds to the name of the index that was used when the table I/O wait event was recorded:

A value of PRIMARY indicates that table I/O used the primary index.
A value of NULL means that table I/O used no index.
Inserts are counted against INDEX_NAME = NULL.

The table_io_waits_summary_by_index_usage table has these indexes:

Unique index on (OBJECT_TYPE, OBJECT_SCHEMA, OBJECT_NAME, INDEX_NAME)

TRUNCATE TABLE is permitted for table I/O summary tables. It resets the summary columns to zero rather than removing rows. This table is also truncated by truncation of the table_io_waits_summary_by_table table. A DDL operation that changes the index structure of a table may cause the per-index statistics to be reset.

27.12.18.8.3 The table_lock_waits_summary_by_table Table

The table_lock_waits_summary_by_table table aggregates all table lock wait events, as generated by the wait/lock/table/sql/handler instrument. The grouping is by table.

This table contains information about internal and external locks:

An internal lock corresponds to a lock in the SQL layer. This is currently implemented by a call to thr_lock(). In event rows, these locks are distinguished by the OPERATION column, which has one of these values:
```
read normal
read with shared locks
read high priority
read no insert
write allow write
write concurrent insert
write delayed
write low priority
write normal
```
An external lock corresponds to a lock in the storage engine layer. This is currently implemented by a call to handler::external_lock(). In event rows, these locks are distinguished by the OPERATION column, which has one of these values:
```
read external
write external
```

The table_lock_waits_summary_by_table table has these grouping columns to indicate how the table aggregates events: OBJECT_TYPE, OBJECT_SCHEMA, and OBJECT_NAME. These columns have the same meaning as in the events_waits_current table. They identify the table to which the row applies.

table_lock_waits_summary_by_table has the following summary columns containing aggregated values. As indicated in the column descriptions, some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. For example, columns that aggregate all locks hold the sum of the corresponding columns that aggregate read and write locks. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.

COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT
These columns aggregate all lock operations. They are the same as the sum of the corresponding xxx_READ and xxx_WRITE columns.
COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ
These columns aggregate all read-lock operations. They are the same as the sum of the corresponding xxx_READ_NORMAL, xxx_READ_WITH_SHARED_LOCKS, xxx_READ_HIGH_PRIORITY, and xxx_READ_NO_INSERT columns.
COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE
These columns aggregate all write-lock operations. They are the same as the sum of the corresponding xxx_WRITE_ALLOW_WRITE, xxx_WRITE_CONCURRENT_INSERT, xxx_WRITE_LOW_PRIORITY, and xxx_WRITE_NORMAL columns.
COUNT_READ_NORMAL, SUM_TIMER_READ_NORMAL, MIN_TIMER_READ_NORMAL, AVG_TIMER_READ_NORMAL, MAX_TIMER_READ_NORMAL
These columns aggregate internal read locks.
COUNT_READ_WITH_SHARED_LOCKS, SUM_TIMER_READ_WITH_SHARED_LOCKS, MIN_TIMER_READ_WITH_SHARED_LOCKS, AVG_TIMER_READ_WITH_SHARED_LOCKS, MAX_TIMER_READ_WITH_SHARED_LOCKS
These columns aggregate internal read locks.
COUNT_READ_HIGH_PRIORITY, SUM_TIMER_READ_HIGH_PRIORITY, MIN_TIMER_READ_HIGH_PRIORITY, AVG_TIMER_READ_HIGH_PRIORITY, MAX_TIMER_READ_HIGH_PRIORITY
These columns aggregate internal read locks.
COUNT_READ_NO_INSERT, SUM_TIMER_READ_NO_INSERT, MIN_TIMER_READ_NO_INSERT, AVG_TIMER_READ_NO_INSERT, MAX_TIMER_READ_NO_INSERT
These columns aggregate internal read locks.
COUNT_READ_EXTERNAL, SUM_TIMER_READ_EXTERNAL, MIN_TIMER_READ_EXTERNAL, AVG_TIMER_READ_EXTERNAL, MAX_TIMER_READ_EXTERNAL
These columns aggregate external read locks.
COUNT_WRITE_ALLOW_WRITE, SUM_TIMER_WRITE_ALLOW_WRITE, MIN_TIMER_WRITE_ALLOW_WRITE, AVG_TIMER_WRITE_ALLOW_WRITE, MAX_TIMER_WRITE_ALLOW_WRITE
These columns aggregate internal write locks.
COUNT_WRITE_CONCURRENT_INSERT, SUM_TIMER_WRITE_CONCURRENT_INSERT, MIN_TIMER_WRITE_CONCURRENT_INSERT, AVG_TIMER_WRITE_CONCURRENT_INSERT, MAX_TIMER_WRITE_CONCURRENT_INSERT
These columns aggregate internal write locks.
COUNT_WRITE_LOW_PRIORITY, SUM_TIMER_WRITE_LOW_PRIORITY, MIN_TIMER_WRITE_LOW_PRIORITY, AVG_TIMER_WRITE_LOW_PRIORITY, MAX_TIMER_WRITE_LOW_PRIORITY
These columns aggregate internal write locks.
COUNT_WRITE_NORMAL, SUM_TIMER_WRITE_NORMAL, MIN_TIMER_WRITE_NORMAL, AVG_TIMER_WRITE_NORMAL, MAX_TIMER_WRITE_NORMAL
These columns aggregate internal write locks.
COUNT_WRITE_EXTERNAL, SUM_TIMER_WRITE_EXTERNAL, MIN_TIMER_WRITE_EXTERNAL, AVG_TIMER_WRITE_EXTERNAL, MAX_TIMER_WRITE_EXTERNAL
These columns aggregate external write locks.

The table_lock_waits_summary_by_table table has these indexes:

Unique index on (OBJECT_TYPE, OBJECT_SCHEMA, OBJECT_NAME)

TRUNCATE TABLE is permitted for table lock summary tables. It resets the summary columns to zero rather than removing rows.