10.20.8.2 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.