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pcache: Erlang Process Based Cache

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pcache uses erlang processes to auto-expire cache items.

pcache is an improved version of the cache described in

Modern Era Update

pcache was my first attempt at a generalized erlang caching framework (based around the paper above) and is still a good reference for one-item-per-process style caching.

For production use, ecache is recommended instead. ecache has more features, compression (because cache items are stored in ets), and helpful stack traces when your backing cache functions fail.


The cache server is designed to memoize a specific Module:Fun. The key in a cache is the Argument passed to Module:Fun/1.

Start a cache:

CacheName = my_cache,
M = database,
F = get_result,
Size = 16,     % 16 MB cache
Time = 300000, % 300k ms = 300s = 5 minute TTL
Server = pcache_server:start_link(CacheName, M, F, Size, Time).

The TTL is an idle timer TTL. Each entry resets to the TTL when accessed. A cache with a five minute TTL will expire an entry when nothing touches it for five minutes. The entry timer resets to the TTL every time an item is read. You need to dirty a key when the result of M:F(Key) will change from what is in the cache.

Use a cache:

Result = pcache:get(my_cache, <<"bob">>).
pcache:dirty(my_cache, <<"bob">>, <<"newvalue">>).  % replace entry for <<"bob">>
pcache:dirty(my_cache, <<"bob">>).  % remove entry from cache
pcache:empty(my_cache).  % remove all entries from cache
RandomValues = pcache:rand(my_cache, 12).
RandomKeys = pcache:rand_keys(my_cache, 12).

Bonus feature: use arbitrary M:F/1 calls in a cache:

Result = pcache:memoize(my_cache, OtherMod, OtherFun, Arg).
pcache:dirty_memoize(my_cache, OtherMod, OtherFun, Arg).  % remove entry from cache

pcache:memoize/4 helps us get around annoying issues of one-cache-per-mod-fun. Your root cache Mod:Fun could be nonsense if you want to use pcache:memoize/4 everywhere.

Short-hand to make a supervisor entry:

SupervisorWorkerTuple = pcache:cache_sup(Name, M, F, Size).


pcache was used in production for years, but has been replaced by ecache for more modern usage.


I originally wrote this in August 2007 and used it for my own projects over a few years before packaging it into a public release in 2010.

Version 1.0

Initial basic release. Supports Erlang versions before 18.0 (uses erlang:now() for TTL math).

Version 2.0

Modern release. Uses os:timestamp() instead of now() for TTL math.

No future improvements are planned. For production use, see ecache instead.


    rebar compile


    rebar eunit suite=pcache


An Erlang cache where every stored item is its own process.



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