MySQL 5.5 Release Notes
Example 14.1 Using the Compression Information Schema Tables
The following is sample output from a database that contains
compressed tables (see Section 14.12, “InnoDB Table Compression”,
INNODB_CMP, and
INNODB_CMPMEM).
The following table shows the contents of
INFORMATION_SCHEMA.INNODB_CMP
under a light workload.
The only compressed page size that the buffer pool contains is
8K. Compressing or uncompressing pages has consumed less than
a second since the time the statistics were reset, because the
columns COMPRESS_TIME and
UNCOMPRESS_TIME are zero.
| page size | compress ops | compress ops ok | compress time | uncompress ops | uncompress time |
|---|---|---|---|---|---|
| 1024 | 0 | 0 | 0 | 0 | 0 |
| 2048 | 0 | 0 | 0 | 0 | 0 |
| 4096 | 0 | 0 | 0 | 0 | 0 |
| 8192 | 1048 | 921 | 0 | 61 | 0 |
| 16384 | 0 | 0 | 0 | 0 | 0 |
According to INNODB_CMPMEM, there
are 6169 compressed 8KB pages in the buffer pool.
The following table shows the contents of
INFORMATION_SCHEMA.INNODB_CMPMEM
under a light workload.
Some memory is unusable due to fragmentation of the
InnoDB memory allocator for compressed
pages: SUM(PAGE_SIZE*PAGES_FREE)=6784. This
is because small memory allocation requests are fulfilled by
splitting bigger blocks, starting from the 16K blocks that are
allocated from the main buffer pool, using the buddy
allocation system. The fragmentation is this low because some
allocated blocks have been relocated (copied) to form bigger
adjacent free blocks. This copying of
SUM(PAGE_SIZE*RELOCATION_OPS) bytes has
consumed less than a second
(SUM(RELOCATION_TIME)=0).