Hi all,
in one of my apps users are working with a lot of entities (~10000) quite
frequently. The entire user session runs inside one UoW. As the UoW caches all
entities it ever reads this leads to memory problems. Loading 10000 entities
allocates ~100MB. This is ok for a short period while the user actually works
with the entities - but the UoW cache holds the entire 100MB for the whole user
session.
So I tried a weak/soft reference cache in UnitOfWorkInstance. This seems to work
but there are some open questions/problems:
- The store and some concerns need to use weak/soft references too. Ok did it.
- If the store uses soft references, then it needs a way to get notified if an
entity has been modified, so that it can make a strong reference to it (in order
to not loose modified state). Currently I dont see a way to let the store know
(without introducing a new method).
- My simple approach introduces a race condition that may lead to lost update in
the worst case. Situation: A reads entity and presents it in the UI. Then GC
reclaims the entity. Then B reads/modifies/commits this entity. Then A reads the
entity again (together with new timestamp from B), modifies something that B has
modified and writes back to the store loosing changes from B.
- Is an UoW supposed to be accessed by concurrent threads? If yes then check/set
entities from cache code in UnitOfWorkInstance needs to be synchronized with the
cache.
Any ideas? And/or are there any other problems/pitfalls I'm missing so far?
Thanks,
Falko
--
Falko Bräutigam
http://polymap.org
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