Cache

Cache

The TimeGate comes with a built-in cache that is activated by default. Change this behavior editing in the configuration file.

Populating the cache:

The cache stores TimeMaps which is the return values of the handler function get_all_mementos() only:

• If the Handler does not have get_all_mementos() implemented, the cache will never be filled.
• If the Handler has both the functions get_all_mementos() and get_memento(), only TimeMap requests will fill the cache. All TimeGate requests will use get_memento() which result will not be cached.

Cache HIT conditions:

• Cached TimeMaps can be used used to respond to a TimeMap request from a client if it is fresh enough. The tolerance for freshness can be defined in the configuration file.
• Cached TimeMap can also be used to respond to a TimeGate requests from a client. In this case, it is not the request's time that must lie within the tolerance bounds, but the requested datetime.

Force Fresh value:

If the request contains the header Cache Control: no-cache, then the TimeGate will not return anything from cache.

Example

Suppose you have a TimeMap that was cached at time T. Suppose you have a tolerance of d seconds. A TimeMap request arrives at time R1. A TimeGate request arrives at time R2 with requested datetime j. This request does not contain the header Cache Control: no-cache.

• A TimeMap request will be served from cache only if it arrives within the tolerance: R1 <= T+d.
• A TimeGate request will be served from cache only if the requested datetime happens within the tolerance: j <= T+d, no matter R2. This means that even if a cached value is old, the cache can still respond to TimeGate requests for requested datetimes that are until time T+d.
• All other requests will be cache misses.

Cache size

There is no "maximum size" parameter. The reason for this is that the cache size will depend on the average size of TimeMaps, which itself depends on the length of each URI-Ms it contains, and their average count. These variables will depend on your system. The cache can be managed using the cache_max_values parameter which will affect indirectly its size.