24.4.3 The INFORMATION_SCHEMA INNODB_BUFFER_PAGE

24.4.3 The INFORMATION_SCHEMA INNODB_BUFFER_PAGE_LRU Table

The INNODB_BUFFER_PAGE_LRU table provides information about the pages in the InnoDB 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.

The INNODB_BUFFER_PAGE_LRU table has the same columns as the INNODB_BUFFER_PAGE table, except that the INNODB_BUFFER_PAGE_LRU table has LRU_POSITION and COMPRESSED columns instead of BLOCK_ID and PAGE_STATE columns.

For related usage information and examples, see Section 14.16.5, “InnoDB INFORMATION_SCHEMA Buffer Pool Tables”.

Warning

Querying the INNODB_BUFFER_PAGE_LRU table can affect performance. Do not query this table 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.

The INNODB_BUFFER_PAGE_LRU table has these columns:

POOL_ID
The buffer pool ID. This is an identifier to distinguish between multiple buffer pool instances.
LRU_POSITION
The position of the page in the LRU list.
SPACE
The tablespace ID; the same value as INNODB_SYS_TABLES.SPACE.
PAGE_NUMBER
The page number.

PAGE_TYPE

The page type. The following table shows the permitted values.

Table 24.6 INNODB_BUFFER_PAGE_LRU.PAGE_TYPE Values

Page Type	Description
`ALLOCATED`	Freshly allocated page
`BLOB`	Uncompressed BLOB page
`COMPRESSED_BLOB2`	Subsequent comp BLOB page
`COMPRESSED_BLOB`	First compressed BLOB page
`EXTENT_DESCRIPTOR`	Extent descriptor page
`FILE_SPACE_HEADER`	File space header
`IBUF_BITMAP`	Insert buffer bitmap
`IBUF_FREE_LIST`	Insert buffer free list
`IBUF_INDEX`	Insert buffer index
`INDEX`	B-tree node
`INODE`	Index node
`RTREE_INDEX`	R-tree index
`SYSTEM`	System page
`TRX_SYSTEM`	Transaction system data
`UNDO_LOG`	Undo log page
`UNKNOWN`	Unknown

FLUSH_TYPE
The flush type.
FIX_COUNT
The number of threads using this block within the buffer pool. When zero, the block is eligible to be evicted.
IS_HASHED
Whether a hash index has been built on this page.
NEWEST_MODIFICATION
The Log Sequence Number of the youngest modification.
OLDEST_MODIFICATION
The Log Sequence Number of the oldest modification.
ACCESS_TIME
An abstract number used to judge the first access time of the page.
TABLE_NAME
The name of the table the page belongs to. This column is applicable only to pages with a PAGE_TYPE value of INDEX.
INDEX_NAME
The name of the index the page belongs to. This can be the name of a clustered index or a secondary index. This column is applicable only to pages with a PAGE_TYPE value of INDEX.
NUMBER_RECORDS
The number of records within the page.
DATA_SIZE
The sum of the sizes of the records. This column is applicable only to pages with a PAGE_TYPE value of INDEX.
COMPRESSED_SIZE
The compressed page size. NULL for pages that are not compressed.
COMPRESSED
Whether the page is compressed.
IO_FIX
Whether any I/O is pending for this page: IO_NONE = no pending I/O, IO_READ = read pending, IO_WRITE = write pending.
IS_OLD
Whether the block is in the sublist of old blocks in the LRU list.
FREE_PAGE_CLOCK
The value of the freed_page_clock counter when the block was the last placed at the head of the LRU list. The freed_page_clock counter tracks the number of blocks removed from the end of the LRU list.

Example

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE_LRU LIMIT 1\G
*************************** 1. row ***************************
            POOL_ID: 0
       LRU_POSITION: 0
              SPACE: 97
        PAGE_NUMBER: 1984
          PAGE_TYPE: INDEX
         FLUSH_TYPE: 1
          FIX_COUNT: 0
          IS_HASHED: YES
NEWEST_MODIFICATION: 719490396
OLDEST_MODIFICATION: 0
        ACCESS_TIME: 3378383796
         TABLE_NAME: `employees`.`salaries`
         INDEX_NAME: PRIMARY
     NUMBER_RECORDS: 468
          DATA_SIZE: 14976
    COMPRESSED_SIZE: 0
         COMPRESSED: NO
             IO_FIX: IO_NONE
             IS_OLD: YES
    FREE_PAGE_CLOCK: 0

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.
Querying this table can require MySQL to allocate a large block of contiguous memory, more than 64 bytes times the number of active pages in the buffer pool. This allocation could potentially cause an out-of-memory error, especially for systems with multi-gigabyte buffer pools.
Querying this table requires MySQL to lock the data structure representing the buffer pool while traversing the LRU list, which can reduce concurrency, especially for systems with multi-gigabyte buffer pools.
When tables, table rows, partitions, or indexes are deleted, associated pages remain in the buffer pool until space is required for other data. The INNODB_BUFFER_PAGE_LRU table reports information about these pages until they are evicted from the buffer pool. For more information about how the InnoDB manages buffer pool data, see Section 14.5.1, “Buffer Pool”.