28.4.26 The INFORMATION_SCHEMA INNODB_TABLESTATS View

The INNODB_TABLESTATS table provides a view of low-level status information about InnoDB tables. This data is used by the MySQL optimizer to calculate which index to use when querying an InnoDB table. This information is derived from in-memory data structures rather than data stored on disk. There is no corresponding internal InnoDB system table.

InnoDB tables are represented in this view if they have been opened since the last server restart and have not aged out of the table cache. Tables for which persistent stats are available are always represented in this view.

Table statistics are updated only for DELETE or UPDATE operations that modify indexed columns. Statistics are not updated by operations that modify only nonindexed columns.

ANALYZE TABLE clears table statistics and sets the STATS_INITIALIZED column to Uninitialized. Statistics are collected again the next time the table is accessed.

For related usage information and examples, see Section 17.15.3, “InnoDB INFORMATION_SCHEMA Schema Object Tables”.

The INNODB_TABLESTATS table has these columns:

• TABLE_ID

  An identifier representing the table for which statistics are available; the same value as INNODB_TABLES.TABLE_ID.

• NAME

  The name of the table; the same value as INNODB_TABLES.NAME.

• STATS_INITIALIZED

  The value is Initialized if the statistics are already collected, Uninitialized if not.

• NUM_ROWS

  The current estimated number of rows in the table. Updated after each DML operation. The value could be imprecise if uncommitted transactions are inserting into or deleting from the table.

• CLUST_INDEX_SIZE

  The number of pages on disk that store the clustered index, which holds the InnoDB table data in primary key order. This value might be null if no statistics are collected yet for the table.

• OTHER_INDEX_SIZE

  The number of pages on disk that store all secondary indexes for the table. This value might be null if no statistics are collected yet for the table.

• MODIFIED_COUNTER

  The number of rows modified by DML operations, such as INSERT, UPDATE, DELETE, and also cascade operations from foreign keys. This column is reset each time table statistics are recalculated

• AUTOINC

  The next number to be issued for any auto-increment-based operation. The rate at which the AUTOINC value changes depends on how many times auto-increment numbers have been requested and how many numbers are granted per request.

• REF_COUNT

  When this counter reaches zero, the table metadata can be evicted from the table cache.

Example

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TABLESTATS where TABLE_ID = 71\G
*************************** 1. row ***************************
         TABLE_ID: 71
             NAME: test/t1
STATS_INITIALIZED: Initialized
         NUM_ROWS: 1
 CLUST_INDEX_SIZE: 1
 OTHER_INDEX_SIZE: 0
 MODIFIED_COUNTER: 1
          AUTOINC: 0
        REF_COUNT: 1

Notes

• This table is useful primarily for expert-level performance monitoring, or when developing performance-related extensions for MySQL.

• You must have the PROCESS privilege to query this table.

• Use the INFORMATION_SCHEMA COLUMNS table or the SHOW COLUMNS statement to view additional information about the columns of this table, including data types and default values.