MySQL 8.4 Release Notes
The INNODB_CMPMEM and
INNODB_CMPMEM_RESET tables provide
status information about compressed pages that reside in the
buffer pool. Please consult Section 17.9, “InnoDB Table and Page Compression”
for further information on compressed tables and the use of the
buffer pool. The INNODB_CMP and
INNODB_CMP_RESET tables should
provide more useful statistics on compression.
Internal Details
InnoDB uses a
buddy allocator
system to manage memory allocated to
pages of various sizes,
from 1KB to 16KB. Each row of the two tables described here
corresponds to a single page size.
The INNODB_CMPMEM and
INNODB_CMPMEM_RESET tables have
identical contents, but reading from
INNODB_CMPMEM_RESET resets the
statistics on relocation operations. For example, if every 60
minutes you archived the output of
INNODB_CMPMEM_RESET, it would show
the hourly statistics. If you never read
INNODB_CMPMEM_RESET and monitored
the output of INNODB_CMPMEM
instead, it would show the cumulative statistics since
InnoDB was started.
For the table definition, see Section 28.4.7, “The INFORMATION_SCHEMA INNODB_CMPMEM and INNODB_CMPMEM_RESET Tables”.