MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide

14.15.5 InnoDB INFORMATION_SCHEMA Buffer Pool Tables

The InnoDB INFORMATION_SCHEMA buffer pool tables provide buffer pool status information and metadata about the pages within the InnoDB buffer pool.

The InnoDB INFORMATION_SCHEMA buffer pool tables include those listed below:

mysql> SHOW TABLES FROM INFORMATION_SCHEMA LIKE 'INNODB_BUFFER%';
+-----------------------------------------------+
| Tables_in_INFORMATION_SCHEMA (INNODB_BUFFER%) |
+-----------------------------------------------+
| INNODB_BUFFER_PAGE_LRU                        |
| INNODB_BUFFER_PAGE                            |
| INNODB_BUFFER_POOL_STATS                      |
+-----------------------------------------------+

Table Overview

Warning

Querying the INNODB_BUFFER_PAGE or INNODB_BUFFER_PAGE_LRU table can affect performance. Do not query these tables on a production system unless you are aware of the performance impact and have determined it to be acceptable. To avoid impacting performance on a production system, reproduce the issue you want to investigate and query buffer pool statistics on a test instance.

Example 14.6 Querying System Data in the INNODB_BUFFER_PAGE Table

This query provides an approximate count of pages that contain system data by excluding pages where the TABLE_NAME value is either NULL or includes a slash / or period . in the table name, which indicates a user-defined table.

mysql> SELECT COUNT(*) FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME IS NULL OR (INSTR(TABLE_NAME, '/') = 0 AND INSTR(TABLE_NAME, '.') = 0);
+----------+
| COUNT(*) |
+----------+
|     1320 |
+----------+

This query returns the approximate number of pages that contain system data, the total number of buffer pool pages, and an approximate percentage of pages that contain system data.

mysql> SELECT
       (SELECT COUNT(*) FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME IS NULL OR (INSTR(TABLE_NAME, '/') = 0 AND INSTR(TABLE_NAME, '.') = 0)
       ) AS system_pages,
       (
       SELECT COUNT(*)
       FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       ) AS total_pages,
       (
       SELECT ROUND((system_pages/total_pages) * 100)
       ) AS system_page_percentage;
+--------------+-------------+------------------------+
| system_pages | total_pages | system_page_percentage |
+--------------+-------------+------------------------+
|         1320 |        8192 |                     16 |
+--------------+-------------+------------------------+

The type of system data in the buffer pool can be determined by querying the PAGE_TYPE value. For example, the following query returns eight distinct PAGE_TYPE values among the pages that contain system data:

mysql> SELECT DISTINCT PAGE_TYPE FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME IS NULL OR (INSTR(TABLE_NAME, '/') = 0 AND INSTR(TABLE_NAME, '.') = 0);
+-------------------+
| PAGE_TYPE         |
+-------------------+
| SYSTEM            |
| IBUF_BITMAP       |
| UNDO_LOG          |
| UNKNOWN           |
| FILE_SPACE_HEADER |
| INODE             |
| ALLOCATED         |
| TRX_SYSTEM        |
+-------------------+

Example 14.7 Querying User Data in the INNODB_BUFFER_PAGE Table

This query provides an approximate count of pages containing user data by counting pages where the TABLE_NAME value is NOT NULL and NOT LIKE '%INNODB_SYS_TABLES%'.

mysql> SELECT COUNT(*) FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME IS NOT NULL;
+----------+
| COUNT(*) |
+----------+
|     6872 |
+----------+

This query returns the approximate number of pages that contain user data, the total number of buffer pool pages, and an approximate percentage of pages that contain user data.

mysql> SELECT
       (SELECT COUNT(*) FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME IS NOT NULL AND (INSTR(TABLE_NAME, '/') > 0 OR INSTR(TABLE_NAME, '.') > 0)
       ) AS user_pages,
       (
       SELECT COUNT(*)
       FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       ) AS total_pages,
       (
       SELECT ROUND((user_pages/total_pages) * 100)
       ) AS user_page_percentage;
+------------+-------------+----------------------+
| user_pages | total_pages | user_page_percentage |
+------------+-------------+----------------------+
|       6872 |        8192 |                   84 |
+------------+-------------+----------------------+

This query identifies user-defined tables with pages in the buffer pool:

mysql> SELECT DISTINCT TABLE_NAME FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME IS NOT NULL AND (INSTR(TABLE_NAME, '/') > 0 OR INSTR(TABLE_NAME, '.') > 0)
       AND TABLE_NAME NOT LIKE '`mysql`.`innodb_%';
+-------------------------+
| TABLE_NAME              |
+-------------------------+
| `employees`.`salaries`  |
| `employees`.`employees` |
+-------------------------+

Example 14.8 Querying Index Data in the INNODB_BUFFER_PAGE Table

For information about index pages, query the INDEX_NAME column using the name of the index. For example, the following query returns the number of pages and total data size of pages for the emp_no index that is defined on the employees.salaries table:

mysql> SELECT INDEX_NAME, COUNT(*) AS Pages,
       ROUND(SUM(IF(COMPRESSED_SIZE = 0, @@GLOBAL.innodb_page_size, COMPRESSED_SIZE))/1024/1024)
       AS 'Total Data (MB)'
       FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE INDEX_NAME='emp_no' AND TABLE_NAME = '`employees`.`salaries`';
+------------+-------+-----------------+
| INDEX_NAME | Pages | Total Data (MB) |
+------------+-------+-----------------+
| emp_no     |  1756 |              27 |
+------------+-------+-----------------+

This query returns the number of pages and total data size of pages for all indexes defined on the employees.salaries table:

mysql> SELECT INDEX_NAME, COUNT(*) AS Pages,
       ROUND(SUM(IF(COMPRESSED_SIZE = 0, @@GLOBAL.innodb_page_size, COMPRESSED_SIZE))/1024/1024)
       AS 'Total Data (MB)'
       FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
       WHERE TABLE_NAME = '`employees`.`salaries`'
       GROUP BY INDEX_NAME;
+------------+-------+-----------------+
| INDEX_NAME | Pages | Total Data (MB) |
+------------+-------+-----------------+
| emp_no     |  1756 |              27 |
| PRIMARY    |  4838 |              76 |
+------------+-------+-----------------+

Example 14.9 Querying LRU_POSITION Data in the INNODB_BUFFER_PAGE_LRU Table

The INNODB_BUFFER_PAGE_LRU table holds information about the pages in the InnoDB buffer pool, in particular how they are ordered that determines which pages to evict from the buffer pool when it becomes full. The definition for this page is the same as for INNODB_BUFFER_PAGE, except this table has an LRU_POSITION column instead of a BLOCK_ID column.

This query counts the number of positions at a specific location in the LRU list occupied by pages of the employees.employees table.

mysql> SELECT COUNT(LRU_POSITION) FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE_LRU
       WHERE TABLE_NAME='`employees`.`employees`' AND LRU_POSITION < 3072;
+---------------------+
| COUNT(LRU_POSITION) |
+---------------------+
|                 275 |
+---------------------+

Example 14.10 Querying the INNODB_BUFFER_POOL_STATS Table

The INNODB_BUFFER_POOL_STATS table provides information similar to SHOW ENGINE INNODB STATUS and InnoDB buffer pool status variables.

mysql> SELECT * FROM information_schema.INNODB_BUFFER_POOL_STATS \G
*************************** 1. row ***************************
                         POOL_ID: 0
                       POOL_SIZE: 8192
                    FREE_BUFFERS: 1024
                  DATABASE_PAGES: 7029
              OLD_DATABASE_PAGES: 2574
         MODIFIED_DATABASE_PAGES: 0
              PENDING_DECOMPRESS: 0
                   PENDING_READS: 0
               PENDING_FLUSH_LRU: 0
              PENDING_FLUSH_LIST: 0
                PAGES_MADE_YOUNG: 173
            PAGES_NOT_MADE_YOUNG: 3721891
           PAGES_MADE_YOUNG_RATE: 0
       PAGES_MADE_NOT_YOUNG_RATE: 0
               NUMBER_PAGES_READ: 1075
            NUMBER_PAGES_CREATED: 12594
            NUMBER_PAGES_WRITTEN: 13525
                 PAGES_READ_RATE: 0
               PAGES_CREATE_RATE: 0
              PAGES_WRITTEN_RATE: 0
                NUMBER_PAGES_GET: 27873240
                        HIT_RATE: 0
    YOUNG_MAKE_PER_THOUSAND_GETS: 0
NOT_YOUNG_MAKE_PER_THOUSAND_GETS: 0
         NUMBER_PAGES_READ_AHEAD: 576
       NUMBER_READ_AHEAD_EVICTED: 0
                 READ_AHEAD_RATE: 0
         READ_AHEAD_EVICTED_RATE: 0
                    LRU_IO_TOTAL: 0
                  LRU_IO_CURRENT: 0
                UNCOMPRESS_TOTAL: 0
              UNCOMPRESS_CURRENT: 0

For comparison, SHOW ENGINE INNODB STATUS output and InnoDB buffer pool status variable output is shown below, based on the same data set.

For more information about SHOW ENGINE INNODB STATUS output, see Section 14.17.3, “InnoDB Standard Monitor and Lock Monitor Output”.

mysql> SHOW ENGINE INNODB STATUS \G
...
----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 137363456; in additional pool allocated 0
Dictionary memory allocated 99725
Buffer pool size   8192
Free buffers       1024
Database pages     7029
Old database pages 2574
Modified db pages  0
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages made young 173, not young 3721891
0.00 youngs/s, 0.00 non-youngs/s
Pages read 1075, created 12594, written 13525
0.00 reads/s, 0.00 creates/s, 0.00 writes/s
No buffer pool page gets since the last printout
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 7029, unzip_LRU len: 0
I/O sum[0]:cur[0], unzip sum[0]:cur[0]
...

For status variable descriptions, see Section 5.1.9, “Server Status Variables”.

mysql> SHOW STATUS LIKE 'Innodb_buffer%';
+---------------------------------------+-------------+
| Variable_name                         | Value       |
+---------------------------------------+-------------+
| Innodb_buffer_pool_dump_status        | not started |
| Innodb_buffer_pool_load_status        | not started |
| Innodb_buffer_pool_pages_data         | 7029        |
| Innodb_buffer_pool_bytes_data         | 115163136   |
| Innodb_buffer_pool_pages_dirty        | 0           |
| Innodb_buffer_pool_bytes_dirty        | 0           |
| Innodb_buffer_pool_pages_flushed      | 13525       |
| Innodb_buffer_pool_pages_free         | 1024        |
| Innodb_buffer_pool_pages_misc         | 139         |
| Innodb_buffer_pool_pages_total        | 8192        |
| Innodb_buffer_pool_read_ahead_rnd     | 0           |
| Innodb_buffer_pool_read_ahead         | 576         |
| Innodb_buffer_pool_read_ahead_evicted | 0           |
| Innodb_buffer_pool_read_requests      | 27873240    |
| Innodb_buffer_pool_reads              | 500         |
| Innodb_buffer_pool_wait_free          | 0           |
| Innodb_buffer_pool_write_requests     | 11966441    |
+---------------------------------------+-------------+