Database Administrator's Guide

Properties of Cached Files

Although caching data benefits server performance, it is important to be aware of the effect of caching data on the recoverability of updates. The state of a cached file after an abnormal server termination depends on the c-tree options in effect for that file. Below is a summary of the effect of caching on each file type:

• TRNLOG files: Caching does not affect recoverability. The server’s transaction processing logic ensures that all committed transactions are recovered in the event of an abnormal server termination.
• PREIMG or non-transaction files: Caching can lead to loss of unwritten cached data in the event of an abnormal server termination. For these file types, the server does not guarantee a persistent version of the unwritten updated cache images exists on disk, so any unwritten cached data is lost in the event of an abnormal server termination.

WRITETHRU (PREIMG and non-transaction files): To minimize loss of cached data, the WRITETHRU attribute can be applied to a PREIMG or non-transaction file. WRITETHRU causes writes to be written through the server’s cache to the file system (for low-level updates) or flushed to disk (for ISAM updates). See WRITETHRU Files.