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.

TRUNCATE TABLE is permitted for summary tables. It resets the counters 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.

The structure of table_io_waits_summary_by_index_usage is 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.

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