You may consider the tables INNODB_CMPMEM and
INNODB_CMPMEM_RESET as the status information on the
compressed pages that reside in the buffer pool. Please consult
Chapter 3, InnoDB Data Compression for further information on
compressed tables and the use of the buffer pool. The tables
INNODB_CMP and INNODB_CMP_RESET should provide more useful
statistics on compression.
The InnoDB Plugin uses a so-called “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.
These two 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 cumulated statistics since InnoDB was started.
Table 6.2. 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. |
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