use ETS as a cache backend on branch `master'

lucafavatella commented 9 years ago

Process reads cache, finds neither calc nor value, writes calc. Are all the previous actions performed atomically?

horvand commented 9 years ago

@lucafavatella You mean the ETS version of insert_new/2 and lookup() are not atomic?

lucafavatella commented 9 years ago

@horvand I cannot look into this more at the moment. I remember Ed and I looked at both ETS and Mnesia as backends (I am aware of insert_new) and 2 different versions of the rules of the semantics at direct contact with cache (eval_something).

In the git history you shall find my partial revert of a commit by Ed on the matter.

What I remember off the top of my head at the moment is that unless either OTP was including https://github.com/erlang/otp/pull/387 (or similar) correctness with ETS was not guaranteed.

Caveats:

I may remembering wrong;
At the time we may still have been concerned with the possibility to implement GC thus even the insert code was written in order not to undermine the possibility to implement GC in the future - and maybe Ed decided to take a different approach to GC (e.g. the ostrich approach).

horvand commented 9 years ago

Introduced a gen_server to serialise inserts. IMHO, this should provide similar guaranteed as the Mnesia version does. However, this means more or less having a global lock on the whole cache for writes.

et4te commented 9 years ago

Do we have ets:take/2 yet? Looks like it has been accepted, also looks like there is a lock there.

esl / ice

use ETS as a cache backend on branch `master' #73