The Ultimate Guide to High Availability with MariaDB

Information Schema INNODB_BUFFER_PAGE_LRU Table

The Information Schema INNODB_BUFFER_PAGE_LRU table contains information about pages in the buffer pool and how they are ordered for eviction purposes.

The PROCESS privilege is required to view the table.

It has the following columns:

ColumnDescription
POOL_IDBuffer Pool identifier. From MariaDB 10.5.1 returns a value of 0, since multiple InnoDB buffer pool instances has been removed.
LRU_POSITIONLRU (Least recently-used), for determining eviction order from the buffer pool.
SPACETablespace identifier. Matches the SPACE value on the INNODB_SYS_TABLES table.
PAGE_NUMBERBuffer pool page number.
PAGE_TYPEPage type; one of allocated (newly-allocated page), index (B-tree node), undo_log (undo log page), inode (index node), ibuf_free_list (insert buffer free list), ibuf_bitmap (insert buffer bitmap), system (system page), trx_system (transaction system data), file_space_header (file space header), extent_descriptor (extent descriptor page), blob (uncompressed blob page), compressed_blob (first compressed blob page), compressed_blob2 (subsequent compressed blob page) or unknown.
FLUSH_TYPEFlush type. 0= FLUSH_KEEP, 1 =FLUSH_RELEASE, 2 = FLUSH_IGNORE_CHANGED, 3= FLUSH_FORCE_WRITE
FIX_COUNTCount of the threads using this block in the buffer pool. When it is zero, the block can be evicted from the buffer pool.
IS_HASHEDWhether or not a hash index has been built on this page.
NEWEST_MODIFICATIONMost recent modification's Log Sequence Number.
OLDEST_MODIFICATIONOldest modification's Log Sequence Number.
ACCESS_TIMEAbstract number representing the time the page was first accessed.
TABLE_NAMETable that the page belongs to.
INDEX_NAMEIndex that the page belongs to, either a clustered index or a secondary index.
NUMBER_RECORDSNumber of records the page contains.
DATA_SIZESize in bytes of all the records contained in the page.
COMPRESSED_SIZECompressed size in bytes of the page, or NULL for pages that aren't compressed.
PAGE_STATEPage state; one of FILE_PAGE (page from a file) or MEMORY (page from an in-memory object) for valid data, or one of NULL, READY_FOR_USE, NOT_USED, REMOVE_HASH.
IO_FIXWhether there is I/O pending for the page; one of IO_NONE (no pending I/O), IO_READ (read pending), IO_WRITE (write pending).
IS_OLDWhether the page is old or not.
FREE_PAGE_CLOCKFreed_page_clock counter, which tracks the number of blocks removed from the end of the LRU list, at the time the block was last placed at the head of the list.

The related INFORMATION_SCHEMA.INNODB_BUFFER_PAGE table contains the same information, but with a block id rather than LRU position.

Example

DESC information_schema.innodb_buffer_page_lru;
+---------------------+---------------------+------+-----+---------+-------+
| Field               | Type                | Null | Key | Default | Extra |
+---------------------+---------------------+------+-----+---------+-------+
| POOL_ID             | bigint(21) unsigned | NO   |     | 0       |       |
| LRU_POSITION        | bigint(21) unsigned | NO   |     | 0       |       |
| SPACE               | bigint(21) unsigned | NO   |     | 0       |       |
| PAGE_NUMBER         | bigint(21) unsigned | NO   |     | 0       |       |
| PAGE_TYPE           | varchar(64)         | YES  |     | NULL    |       |
| FLUSH_TYPE          | bigint(21) unsigned | NO   |     | 0       |       |
| FIX_COUNT           | bigint(21) unsigned | NO   |     | 0       |       |
| IS_HASHED           | varchar(3)          | YES  |     | NULL    |       |
| NEWEST_MODIFICATION | bigint(21) unsigned | NO   |     | 0       |       |
| OLDEST_MODIFICATION | bigint(21) unsigned | NO   |     | 0       |       |
| ACCESS_TIME         | bigint(21) unsigned | NO   |     | 0       |       |
| TABLE_NAME          | varchar(1024)       | YES  |     | NULL    |       |
| INDEX_NAME          | varchar(1024)       | YES  |     | NULL    |       |
| NUMBER_RECORDS      | bigint(21) unsigned | NO   |     | 0       |       |
| DATA_SIZE           | bigint(21) unsigned | NO   |     | 0       |       |
| COMPRESSED_SIZE     | bigint(21) unsigned | NO   |     | 0       |       |
| COMPRESSED          | varchar(3)          | YES  |     | NULL    |       |
| IO_FIX              | varchar(64)         | YES  |     | NULL    |       |
| IS_OLD              | varchar(3)          | YES  |     | NULL    |       |
| FREE_PAGE_CLOCK     | bigint(21) unsigned | NO   |     | 0       |       |
+---------------------+---------------------+------+-----+---------+-------+

SELECT * FROM INFORMATION_SCHEMA.INNODB_BUFFER_PAGE_LRU\G
...
*************************** 6. row ***************************
            POOL_ID: 0
       LRU_POSITION: 5
              SPACE: 0
        PAGE_NUMBER: 11
          PAGE_TYPE: INDEX
         FLUSH_TYPE: 1
          FIX_COUNT: 0
          IS_HASHED: NO
NEWEST_MODIFICATION: 2046835
OLDEST_MODIFICATION: 0
        ACCESS_TIME: 2585566280
         TABLE_NAME: `SYS_INDEXES`
         INDEX_NAME: CLUST_IND
     NUMBER_RECORDS: 57
          DATA_SIZE: 4016
    COMPRESSED_SIZE: 0
         COMPRESSED: NO
             IO_FIX: IO_NONE
             IS_OLD: NO
    FREE_PAGE_CLOCK: 0
...

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