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From Vikas Saurabh <vikas.saur...@gmail.com>
Subject [Document Cache Size] Is it better to have cache size using number of entries
Date Mon, 18 Aug 2014 10:05:30 GMT
Hi,

We were struggling past couple of weeks with severe performance issues
on AEM6/Oak/MongoNS -- fortunately the issue was due to VM we were
using. So, all seems well for now.

BUT, during investigation, one of the things that we were worried
about was document cache missing hits... we tried modifying its value
to increase cache size to be put at 1GB.

Although, that didn't quite help as the issue wasn't about cache
size... but what worried us more was there was no good way for us to
specify a cache size. While I agree that cache should be a memory
hog... but entry size of a document in cache is quite variable in
nature and as an admin I can make guesses about JCR nodes and their
access patters. Document size, otoh, would vary even during the
lifetime of repository.

Moreover, the only downside (assuming RAM is cheap) of increasing
cache to large number is making cache invalidation expensize.

So, IMHO, document caches should be limited in terms of number of
entries in cache. And if we still want to have byte size limitation,
we can probably have both and cache respects whichever constraint hits
first (sort of min(byte size, entry size)).

We can log an issue for this and provide a patch too -- but it seemed
better to have a conversation going before that.

Thought?

Thanks,
Vikas

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