During a database transaction, information about all database activity occurring during that transaction is written to a before-image (BI) file. WebSpeed maintains one BI file for each database. The information written to the before-image file is carefully coordinated with the timing of the data written to the actual database table. That way, if an error occurs during the database transaction, WebSpeed uses this before-image file to restore the database to the condition it was in before the transaction started. Information written to the before-image file is not buffered. It is written to disk immediately.
Space in the before-image file is allocated in units called clusters. WebSpeed automatically allocates new clusters as needed. (You can use the PROUTIL TRUNCATE BI utility to set the cluster size.) After all changes associated with a cluster have been committed and written to disk, WebSpeed can reuse the cluster. Therefore the disk space used by the before-image file depends on several factors including the cluster size, the scope of your database transactions, and when physical writes are made to the database (.db) file.
