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
INNODB_BUFFER_PAGE
: Holds information about each page in theInnoDB
buffer pool.INNODB_BUFFER_PAGE_LRU
: Holds information about the pages in theInnoDB
buffer pool, in particular how they are ordered in the LRU list that determines which pages to evict from the buffer pool when it becomes full. TheINNODB_BUFFER_PAGE_LRU
table has the same columns as theINNODB_BUFFER_PAGE
table, except that theINNODB_BUFFER_PAGE_LRU
table has anLRU_POSITION
column instead of aBLOCK_ID
column.INNODB_BUFFER_POOL_STATS
: Provides buffer pool status information. Much of the same information is provided bySHOW ENGINE INNODB STATUS
output, or may be obtained usingInnoDB
buffer pool server status variables.
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 17.6 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(*) |
+----------+
| 1516 |
+----------+
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 |
+--------------+-------------+------------------------+
| 295 | 8192 | 4 |
+--------------+-------------+------------------------+
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 |
| UNKNOWN |
| FILE_SPACE_HEADER |
| INODE |
| UNDO_LOG |
| ALLOCATED |
+-------------------+
Example 17.7 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_TABLES%'
.
mysql> SELECT COUNT(*) FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE
WHERE TABLE_NAME IS NOT NULL AND TABLE_NAME NOT LIKE '%INNODB_TABLES%';
+----------+
| COUNT(*) |
+----------+
| 7897 |
+----------+
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 |
+------------+-------------+----------------------+
| 7897 | 8192 | 96 |
+------------+-------------+----------------------+
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 17.8 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 | 1609 | 25 |
+------------+-------+-----------------+
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 | 1608 | 25 |
| PRIMARY | 6086 | 95 |
+------------+-------+-----------------+
Example 17.9 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) |
+---------------------+
| 548 |
+---------------------+
Example 17.10 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: 1
DATABASE_PAGES: 8173
OLD_DATABASE_PAGES: 3014
MODIFIED_DATABASE_PAGES: 0
PENDING_DECOMPRESS: 0
PENDING_READS: 0
PENDING_FLUSH_LRU: 0
PENDING_FLUSH_LIST: 0
PAGES_MADE_YOUNG: 15907
PAGES_NOT_MADE_YOUNG: 3803101
PAGES_MADE_YOUNG_RATE: 0
PAGES_MADE_NOT_YOUNG_RATE: 0
NUMBER_PAGES_READ: 3270
NUMBER_PAGES_CREATED: 13176
NUMBER_PAGES_WRITTEN: 15109
PAGES_READ_RATE: 0
PAGES_CREATE_RATE: 0
PAGES_WRITTEN_RATE: 0
NUMBER_PAGES_GET: 33069332
HIT_RATE: 0
YOUNG_MAKE_PER_THOUSAND_GETS: 0
NOT_YOUNG_MAKE_PER_THOUSAND_GETS: 0
NUMBER_PAGES_READ_AHEAD: 2713
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 17.17.3, “InnoDB Standard Monitor and Lock Monitor Output”.
mysql> SHOW ENGINE INNODB STATUS \G
...
----------------------
BUFFER POOL AND MEMORY
----------------------
Total large memory allocated 137428992
Dictionary memory allocated 579084
Buffer pool size 8192
Free buffers 1
Database pages 8173
Old database pages 3014
Modified db pages 0
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages made young 15907, not young 3803101
0.00 youngs/s, 0.00 non-youngs/s
Pages read 3270, created 13176, written 15109
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: 8173, unzip_LRU len: 0
I/O sum[0]:cur[0], unzip sum[0]:cur[0]
...
For status variable descriptions, see Section 7.1.10, “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_resize_status | not started |
| Innodb_buffer_pool_pages_data | 8173 |
| Innodb_buffer_pool_bytes_data | 133906432 |
| Innodb_buffer_pool_pages_dirty | 0 |
| Innodb_buffer_pool_bytes_dirty | 0 |
| Innodb_buffer_pool_pages_flushed | 15109 |
| Innodb_buffer_pool_pages_free | 1 |
| Innodb_buffer_pool_pages_misc | 18 |
| Innodb_buffer_pool_pages_total | 8192 |
| Innodb_buffer_pool_read_ahead_rnd | 0 |
| Innodb_buffer_pool_read_ahead | 2713 |
| Innodb_buffer_pool_read_ahead_evicted | 0 |
| Innodb_buffer_pool_read_requests | 33069332 |
| Innodb_buffer_pool_reads | 558 |
| Innodb_buffer_pool_wait_free | 0 |
| Innodb_buffer_pool_write_requests | 11985961 |
+---------------------------------------+-------------+