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. 

## Example 

• UNCOMPRESS_TIME 

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

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 

