In web and server-side development, a memcache is a remote service that keeps transient data in temporary, in-memory store and allows for fast access. It is usually based on keys which identify values being stored and retrieved. Due to storing technique – RAM rather than actual disks – it offers great speed (often less than few milliseconds per operation) while introducing a possibility for values to be evicted (deleted) if memcache runs out of space. Should that happen, oldest values are usually disposed of first.
This functionality makes memcache a good secondary storage that complements the usual persistent database, increasing the efficiency of the system as a whole. The usual scenario is to poll memcache first, and resort to querying the database only if the result cannot be found in cache. Once the query is made, its results are memcached for some reasonable amount time (usually called TTL: time to live), depending on allowed trade-offs between speed and being up-to-date with our results.
While making applications more responsive is the primary use case for memcache, it turns out that we can also utilize it for something completely different. That’s because memcache implementations offer something more besides the obvious get/set commands. They also have operations which make it possible to use memcache as synchronization facility.