FairCom DB provides its own caching. By integrating this caching with the logic of the core engine, flushing of the cache can be coordinated with transaction logs. Transaction control is turned on when creating the file by setting the file mode or storage attributes. A utility (cttrnmod) can be used to change the modes of existing files.
When a file is under transaction control, nothing is placed into cache until the transaction is committed. (The transaction is held in temporary memory, called PreImage, until it is complete.) Although there is some overhead from transaction control, this cache provides good performance while maintaining data integrity.
Three different levels of transaction processing are provided by FairCom DB: Full, PreImage, and None. Your choice of transaction control affects both performance and recoverability. The next section describes these modes in detail.