track (version 1.1.9)

track.performance: Performance tuning with track.

Description

Performance tuning with track involves trading off memory use for faster access times to objects. Access time is fastest when all objects are cached in memory, but memory can be exhausted if this is done. Memory use is minimized when objects are not cached in memory at all, but then a file must be read or written each time an object is referenced, and the whole file must be read or written even if only a small part of the object is actually used or changed.

The default mode of operation of track balances memory use and access times by keeping objects in memory for the duration of a top-level task, and flushing them out at the end of the task.

Three options (see track.options) control performance:

• cache: TRUE/FALSE should variables be cached at all?
• cachePolicy: tltPurge/none higher level policy for maintaining cache
• writeToDisk: TRUE/FALSE should objects be written after a change?

Useful possible combinations of settings are:

• cache=TRUE, cachePolicy="tltPurge", writeToDisk=TRUE: (DEFAULT) keep objects in memory for the duration of a task; flush and/or write to disk at the end of task
• cache=TRUE, cachePolicy="none", writeToDisk=TRUE: keep all objects in memory until removed with track.flush; write changed objects to disk immediately
• cache=TRUE, cachePolicy="none", writeToDisk=FALSE: keep all objects in memory until removed with track.flush; don't automatically write changed objects to disk (use track.save)
• cache=FALSE, cachePolicy="none", writeToDisk=TRUE: keep no objects in memory; write changed objects to disk immediately

Performance tuning is a possible area of future development of the track package, at as version 0.9-9, the defaults settings of cache=TRUE, cachePolicy="tltPurge", and writeToDisk=TRUE work well. However, smarter caching based on access patterns to objects is certainly possible.

See Also

Overview and design of the track package.