6.2.1. INNODB_CMP and INNODB_CMP_RESET

The tables INNODB_CMP and INNODB_CMP_RESET contain status information on the operations related to compressed tables, which are covered in Chapter 3, InnoDB Data Compression. The compressed page size is in the column PAGE_SIZE.

These two tables have identical contents, but reading from INNODB_CMP_RESET resets the statistics on compression and uncompression operations. For example, if you archived the output of INNODB_CMP_RESET every 60 minutes, it would show the hourly statistics. If you never read INNODB_CMP_RESET and monitored the output of INNODB_CMP instead, it would show the cumulated statistics since InnoDB was started.

Table 6.1. Columns of INNODB_CMP and INNODB_CMP_RESET

Column nameDescription
PAGE_SIZECompressed page size in bytes.
COMPRESS_OPSNumber of times a B-tree page of the size PAGE_SIZE has been compressed. Pages are compressed whenever an empty page is created or the space for the uncompressed modification log runs out.
COMPRESS_OPS_OKNumber of times a B-tree page of the size PAGE_SIZE has been successfully compressed. This count should never exceed COMPRESS_OPS.
COMPRESS_TIMETotal time in seconds spent in attempts to compress B-tree pages of the size PAGE_SIZE.
UNCOMPRESS_OPSNumber of times a B-tree page of the size PAGE_SIZE has been uncompressed. B-tree pages are uncompressed whenever compression fails or at first access when the uncompressed page does not exist in the buffer pool.
UNCOMPRESS_TIMETotal time in seconds spent in uncompressing B-tree pages of the size PAGE_SIZE.


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