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MySQL 5.7 Reference Manual  /  ...  /  The INFORMATION_SCHEMA INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET Tables

24.32.6 The INFORMATION_SCHEMA INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET Tables

The INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET tables provide status information on operations related to compressed InnoDB tables and indexes, with separate statistics for each combination of database, table, and index, to help you evaluate the performance and usefulness of compression for specific tables.

For a compressed InnoDB table, both the table data and all the secondary indexes are compressed. In this context, the table data is treated as just another index, one that happens to contain all the columns: the clustered index.

The INNODB_CMP_PER_INDEX and INNODB_CMP_PER_INDEX_RESET tables have these columns:

  • DATABASE_NAME

    The schema (database) containing the applicable table.

  • TABLE_NAME

    The table to monitor for compression statistics.

  • INDEX_NAME

    The index to monitor for compression statistics.

  • COMPRESS_OPS

    The number of compression operations attempted. Pages are compressed whenever an empty page is created or the space for the uncompressed modification log runs out.

  • COMPRESS_OPS_OK

    The number of successful compression operations. Subtract from the COMPRESS_OPS value to get the number of compression failures. Divide by the COMPRESS_OPS value to get the percentage of compression failures.

  • COMPRESS_TIME

    The total time in seconds used for compressing data in this index.

  • UNCOMPRESS_OPS

    The number of uncompression operations performed. Compressed InnoDB pages are uncompressed whenever compression fails, or the first time a compressed page is accessed in the buffer pool and the uncompressed page does not exist.

  • UNCOMPRESS_TIME

    The total time in seconds used for uncompressing data in this index.

Example

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_CMP_PER_INDEX\G
*************************** 1. row ***************************
  database_name: employees
     table_name: salaries
     index_name: PRIMARY
   compress_ops: 0
compress_ops_ok: 0
  compress_time: 0
 uncompress_ops: 23451
uncompress_time: 4
*************************** 2. row ***************************
  database_name: employees
     table_name: salaries
     index_name: emp_no
   compress_ops: 0
compress_ops_ok: 0
  compress_time: 0
 uncompress_ops: 1597
uncompress_time: 0

Notes


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