Information Schema INNODB_CMP and INNODB_CMP_RESET Tables

The INNODB_CMP and INNODB_CMP_RESET tables contain status information on compression operations related to compressed XtraDB/InnoDB tables.

The PROCESS privilege is required to query this table.

These tables contain the following columns:

Column NameDescription
PAGE_SIZECompressed page size, in bytes. This value is unique in the table; other values are totals which refer to pages of this size.
COMPRESS_OPSHow many times a page of the size PAGE_SIZE has been compressed. This happens when a new page is created because the compression log runs out of space. This value includes both successful operations and compression failures.
COMPRESS_OPS_OKHow many times a page of the size PAGE_SIZE has been successfully compressed. This value should be as close as possible to COMPRESS_OPS. If it is notably lower, either avoid compressing some tables, or increase the KEY_BLOCK_SIZE for some compressed tables.
COMPRESS_TIMETime (in seconds) spent to compress pages of the size PAGE_SIZE. This value includes time spent in compression failures.
UNCOMPRESS_OPSHow many times a page of the size PAGE_SIZE has been uncompressed. This happens when an uncompressed version of a page is created in the buffer pool, or when a compression failure occurs.
UNCOMPRESS_TIMETime (in seconds) spent to uncompress pages of the size PAGE_SIZE.

These tables can be used to measure the effectiveness of XtraDB/InnoDB table compression. When you have to decide a value for KEY_BLOCK_SIZE, you can create more than one version of the table (one for each candidate value) and run a realistic workload on them. Then, these tables can be used to see how the operations performed with different page sizes.

INNODB_CMP and INNODB_CMP_RESET have the same columns and always contain the same values, but when INNODB_CMP_RESET is queried, both the tables are cleared. INNODB_CMP_RESET can be used, for example, if a script periodically logs the performances of compression in the last period of time. INNODB_CMP can be used to see the cumulated statistics.


SELECT * FROM information_schema.INNODB_CMP\G
**************************** 1. row *****************************
      page_size: 1024
   compress_ops: 0
compress_ops_ok: 0
  compress_time: 0
 uncompress_ops: 0
uncompress_time: 0

See Also

Other tables that can be used to monitor XtraDB/InnoDB compressed tables:


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