Product Documentation

Database Administrator's Guide

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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.