Java Performance Tuning

Cached Access

Caches use local data when present, and thus don’t need to access nonlocal data. If the data is not present locally, the nonlocal data must be accessed or calculated; this is then stored locally as well as being returned. So after the first access, the data is then available locally, and access is quicker. How much quicker depends on the type of cache.

Most caches have to maintain the consistency of the data held in the cache: it is usually important for the data in the cache to be up to date. When considering the use of a cache, bear in mind the expected lifetime of the data and any refresh rate or time-to-live values associated with the data. Similarly, for output data, consider how long to keep data in the cache before it must be written out. You may have differing levels of priority for writing out different types of data. For example, some filesystems keep general written data in a write cache, but immediately write critical system data that ensures system consistency in case of crashes. Also, as caches cannot usually hold all the data you would like, a strategy for swapping data out of the cache to overcome cache space limitations is usually necessary. The memory used by the cache is often significant, and it is always better to release the resources used by it explicitly when it is no longer needed, or reduce resources being used by the cache when possible, even if the cache itself is still required.

Caching can apply to data held in single objects or groups ...