See Also Connector/J, Connector/NET, exception interceptor, interceptor, statement interceptor. 

## commit 

 A SQL  statement that ends a transaction , making permanent any changes made by the transaction. It is the opposite of rollback , which undoes any changes made in the transaction. 

InnoDB  uses an optimistic  mechanism for commits, so that changes can be written to the data files before the commit actually occurs. This technique makes the commit itself faster, with the tradeoff that more work is required in case of a rollback. 

By default, MySQL uses the autocommit  setting, which automatically issues a commit following each SQL statement. 

See Also autocommit, optimistic, rollback, SQL, transaction. 

## compact row format 

 A row format  for InnoDB tables. It was the default row format from MySQL 5.0.3 to MySQL 5.7.8. In MySQL 8.0, the default row format is defined by the innodb_default_row_format  configuration option, which has a default setting of DYNAMIC . The COMPACT  row format provides a more compact representation for nulls and variable-length columns than the REDUNDANT  row format. 

For additional information about InnoDB COMPACT  row format, see Section 15.10, “InnoDB Row Formats” . See Also dynamic row format, file format, redundant row format, row format. 

## composite index 

 An index  that includes multiple columns. 

See Also index. 

## compressed backup 

 The compression feature of the MySQL Enterprise Backup  product makes a compressed copy of each tablespace, changing the extension from .ibd  to .ibz . Compressing backup data allows you to keep more backups on hand, and reduces the time to transfer backups to a different server. The data is uncompressed during the restore operation. When a compressed backup operation processes a table that is already compressed, it skips the compression step for that table, because compressing again would result in little or no space savings. 

A set of files produced by the MySQL Enterprise Backup  product, where each tablespace  is compressed. The compressed files are renamed with a .ibz  file extension. 

Applying compression  at the start of the backup process helps to avoid storage overhead during the compression process, and to avoid network overhead when transferring the backup files to another server. The process of applying  the binary log  takes longer, and requires uncompressing the backup files. 

See Also apply, binary log, compression, hot backup, MySQL Enterprise Backup, tablespace. 

## compressed row format 

 A row format  that enables data and index compression  for InnoDB  tables. Large fields are stored away from the page that holds the rest of the row data, as in dynamic row format . Both index pages and the large fields are compressed, yielding memory and disk savings. Depending on the structure of the data, the decrease in memory and disk usage might or might not outweigh the performance overhead of uncompressing the data as it is used. See Section 15.9, “InnoDB Table and Page Compression”  for usage details. 

For additional information about InnoDB COMPRESSED  row format, see DYNAMIC Row Format. 

See Also compression, dynamic row format, row format. 

## compressed table 

 A table for which the data is stored in compressed form. For InnoDB , it is a table created with ROW_FORMAT=COMPRESSED . See Section 15.9, “InnoDB Table and Page Compression”  for more information. 

