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https://issues.apache.org/jira/browse/GEODE-6636?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mario Ivanac resolved GEODE-6636.
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Resolution: Fixed
> Buffers.acquireBuffer is not optimal
> ------------------------------------
>
> Key: GEODE-6636
> URL: https://issues.apache.org/jira/browse/GEODE-6636
> Project: Geode
> Issue Type: Improvement
> Components: core
> Reporter: Darrel Schneider
> Assignee: Mario Ivanac
> Priority: Major
> Labels: needs-review, performance, pull-request-available
> Time Spent: 5h 20m
> Remaining Estimate: 0h
>
> org.apache.geode.internal.net.Buffers.acquireBuffer takes buffers out of a
> ConcurrentLinkedQueue. If the buffer is too small then it adds it back to the
> queue and adds it to an IdentityHashMap. The map is just to detect if we have
> looped around and found one we added to the map in a previous iteration.
> A more efficient way to do this, which will only remove things from the queue
> that we will either throw away or use and return later, and which gets rid of
> the map, is to use ConcurrentLinkedQueue.remove(Object). You can see an
> example of this by looking at:
> AvailableConnectionManager.EqualsWithPredicate. The predicate to use with
> acquireBuffer is that the soft reference is null or that the capacity of the
> referenced buffer is large enough. If you remove one because the reference is
> null then you need to call remove(Object) again (after decrementing the
> correct stat) since all you did was find one that had been garbage collected.
> You want to keep the predicate as cheap as possible since it is called in the
> "compare-and-set" spin loop. The more you do in the predicate, the more
> likely a concurrent thread will take that buffer and you will need to spin
> around and try again.
> I was surprised when running a benchmark under the profiler to see operations
> on this IdentityHashMap show up. The benchmark was doing pr puts of all the
> same size so I would have thought all these direct buffers would be the same.
> I think it would be worth understanding what sizes of buffers will be
> requested by acquireBuffer and how often they will be acquired and returned.
> If different sizes is a normal use case then it probably would make sense to
> have more than one queue. If we could go to a queue knowing that if it has a
> buffer in it that it meets are desired size. The geode off-heap free list
> implementation does this and only the largest allocations need to search
> through a free list that has items in it that exceed a max size. Every other
> free list is found quickly be using the requested size to index an array of
> free lists, which only contain items of that size.
>
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