The INNODB_CMPMEM and
INNODB_CMPMEM_RESET tables contain status
information on compressed pages within the
InnoDB buffer pool.
Table 21.5 Columns of INNODB_CMPMEM and INNODB_CMPMEM_RESET
| Column name | Description |
|---|---|
PAGE_SIZE | Block size in bytes. Each record of this table describes blocks of this size. |
BUFFER_POOL_INSTANCE | A unique identifier for the buffer pool instance. |
PAGES_USED | Number of blocks of the size PAGE_SIZE that are
currently in use. |
PAGES_FREE | Number of blocks of the size PAGE_SIZE that are
currently available for allocation. This column shows the
external fragmentation in the memory pool. Ideally, these
numbers should be at most 1. |
RELOCATION_OPS | Number of times a block of the size PAGE_SIZE has
been relocated. The buddy system can relocate the
allocated “buddy neighbor” of a freed block
when it tries to form a bigger freed block. Reading from
the table INNODB_CMPMEM_RESET resets
this count. |
RELOCATION_TIME | Total time in microseconds spent in relocating blocks of the size
PAGE_SIZE. Reading from the table
INNODB_CMPMEM_RESET resets this count. |
Example:
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_CMPMEM\G
*************************** 1. row ***************************
page_size: 1024
buffer_pool_instance: 0
pages_used: 0
pages_free: 0
relocation_ops: 0
relocation_time: 0
*************************** 2. row ***************************
page_size: 2048
buffer_pool_instance: 0
pages_used: 0
pages_free: 0
relocation_ops: 0
relocation_time: 0
*************************** 3. row ***************************
page_size: 4096
buffer_pool_instance: 0
pages_used: 0
pages_free: 0
relocation_ops: 0
relocation_time: 0
*************************** 4. row ***************************
page_size: 8192
buffer_pool_instance: 0
pages_used: 9043
pages_free: 1
relocation_ops: 2457
relocation_time: 0
*************************** 5. row ***************************
page_size: 16384
buffer_pool_instance: 0
pages_used: 0
pages_free: 0
relocation_ops: 0
relocation_time: 0
Notes:
Use these tables to measure the effectiveness of
InnoDB table compression in your database.
Use DESCRIBE or
SHOW COLUMNS to view additional
information about the columns of these tables including data
types and default values.
You must have the PROCESS
privilege to query this table.
For usage information, see Section 14.18.1.3, “Using the Compression Information Schema Tables”.