20.28.2. The INFORMATION_SCHEMA INNODB_CMPMEM and
INNODB_CMPMEM_RESET Tables
The INNODB_CMPMEM and
INNODB_CMPMEM_RESET tables contain status
information on compressed pages within the
InnoDB buffer pool.
Table 20.2. 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.
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.
Notes:
Use these tables to measure the effectiveness of
InnoDB table compression in your database.
You must have the PROCESS privilege to
query this table.
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