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25.39.27 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 15.14.3, “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 recalculatedAUTOINC
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
- *************************** 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 theSHOW COLUMNS
statement to view additional information about the columns of this table, including data types and default values.
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Document créé le 26/06/2006, dernière modification le 26/10/2018
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