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From ramkrishna vasudevan <ramkrishna.s.vasude...@gmail.com>
Subject Re: Off-heap block cache fails in 0.94.6
Date Fri, 24 Jan 2014 06:20:22 GMT
Hi Dean

There is a patch attached in
https://issues.apache.org/jira/browse/HBASE-6048 by Chunhui.  Hope it
addresses your problem.  Can you take a look at it and see if it is working


On Fri, Jan 24, 2014 at 10:16 AM, ramkrishna vasudevan <
ramkrishna.s.vasudevan@gmail.com> wrote:

> Hi Dean
> I mentioned those JIRAs to highlight the fact that the bug was open and it
> was not fixed.  I think better we fix this in 0.94 also, so that users
> using this feature do not run into surprises.  And we are sorry that the
> feature that worked well for you in 0.92, did not work out in 0.94.  It
> should be resolved IMO.
> You are going for a patch from your side?  If so, that would be great.
> Regards
> Ram
> On Thu, Jan 23, 2014 at 11:31 PM, Dean <hikeonpast@gmail.com> wrote:
>> Hi Ramkrishna,
>> I had taken the experimental label to mean "use at your own risk" when
>> the feature was released in 0.92.  After some judicious testing in the
>> spirit of "use at your own risk", we found the feature worked well for our
>> use case.  In 0.94, we had expected off-heap cache to be the same as 0.92,
>> or perhaps even with a few small improvements. It came as a bit of a
>> surprise that the feature went from experimental to plain broken.
>> Perhaps my interpretation of "experimental" was off base to begin with -
>> in retrospect it may have been presumptuous to assume that an
>> "experimental" feature would only become more mature and eventually
>> graduate to a full-fledged feature.  I can see how such a feature might go
>> the other way, quietly going from experimental to deprecated to broken.
>> We'd love a viable off-heap cache solution - we're currently scrambling a
>> bit for options in production since we're not able to roll back to 0.92.1.
>>  The HBASE-7404 solution that Ted pointed out looks awesome, but we're not
>> in a position to move to 0.96 to take advantage of it.  At this point, I'm
>> fishing for options.  We run a mix of random reads and scans.  We disable
>> block cache for scans to improve random read performance.  With a chunk of
>> RAM allocated to off-heap cache, this seemed to work well.  Now that we're
>> dominated by filesystem cache, scans with block cache disabled still trash
>> the cache, significantly hurting our random read performance.  We've got
>> short-circuit reads and Hbase checksums enabled in an attempt to gain back
>> some of the lost perf, but they are more of a band-aid than a fix for root
>> cause.  Any suggestions are much appreciated.
>> Cheers,
>> Dean

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