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From Vikas Saurabh <vikas.saur...@gmail.com>
Subject Re: [Document Cache Size] Is it better to have cache size using number of entries
Date Mon, 18 Aug 2014 14:25:24 GMT
>> we can probably have both and cache respects whichever constraint hits
>> first (sort of min(byte size, entry size)).
> First of all I don't know MongoNS implementation details so I can be wrong.
>
> I'd rather keep the size in bytes as it gives me much more control over
> the memory I have and what I decide to provide to the application. If we
> say, to take an extreme example, 1 document only in cache and then this
> single document exceed the amount of available memory I fear an OOM. On
> the other hand having bytes ensure us the application keeps working and
> it will be task of a sysadmin to monitor the eventual hit/miss ratio to
> adjust the cache accordingly.
>
Yes, sysadmin can modify cache size in bytes if miss ratio increases.
But, in current scenario, I couldn't figure out a neat way
(heuristic/guesswork) to figure
out if it's application mis-behavior or lack of cache size (notice our
issue didn't happen
to be related to cache size... but still the question did bug us). On
the other hand, an
sysadmin can be provided with a rough idea about relation of
(frequently used) repo nodes
using which sysadmin can update cache size.
Also, I do take the point of avoiding OOMs in case of pretty large
documents which is why
we can have both properties(byte size and entry count) with byte
constraint being a fail safe.

Thanks,
Vikas

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