Preallocating space in journal files using alterdb can reduce the likelihood of running out of journal file disk space.

Filling a journal file causes the archiver to stop, and if left untreated, eventually causes the log file to fill, which brings the system to a halt.

With the alter database operation you can, for example, request creation of journal files of a given size and also request preallocation of the entire file. If the file is sufficiently large, this eliminates the possibility of running out of journal disk space during normal online processing.

This can, however, cause unused journal space to be wasted. If excessive space is allocated during journal file creation, that disk space can be made unavailable when a subsequent checkpoint operation takes place.

If it is necessary to control journal file size more accurately, the archiver must be awakened more frequently. This can be accomplished with smaller consistency point (CP) intervals, allowing more frequent archiver “wake-ups.” The consistency point interval can be configured using CBF (or the Configuration Manager, if available). Smaller CP intervals can affect system performance, although the processing involved is for a short interval of time.