Documentation Home
MySQL 5.5 Reference Manual
Related Documentation Download this Manual
PDF (US Ltr) - 27.2Mb
PDF (A4) - 27.2Mb
PDF (RPM) - 25.8Mb
HTML Download (TGZ) - 6.5Mb
HTML Download (Zip) - 6.6Mb
HTML Download (RPM) - 5.6Mb
Man Pages (TGZ) - 158.6Kb
Man Pages (Zip) - 262.1Kb
Info (Gzip) - 2.6Mb
Info (Zip) - 2.6Mb
Excerpts from this Manual Using the Compression Information Schema Tables

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).

page size pages used pages free relocation ops relocation time
1024 0 0 0 0
2048 0 1 0 0
4096 0 1 0 0
8192 6169 0 5 0
16384 0 0 0 0

User Comments
User comments in this section are, as the name implies, provided by MySQL users. The MySQL documentation team is not responsible for, nor do they endorse, any of the information provided here.
Sign Up Login You must be logged in to post a comment.