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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Read Performance
Date Wed, 31 Mar 2010 22:05:30 GMT
Yes, I would.  How many columns are you reading per row?  How larger
are they?  Are they supercolumns?

On Wed, Mar 31, 2010 at 4:54 PM, James Golick <jamesgolick@gmail.com> wrote:
> I just tried running the same multi_get against cassandra 1000 times,
> assuming that that'd force it in to cache.
> I'm definitely seeing a 5-10ms improvement, but it's still looking like
> 20-30ms on average. Would you expect it to be faster than that?
> - James
>
> On Wed, Mar 31, 2010 at 11:44 AM, Jonathan Ellis <jbellis@gmail.com> wrote:
>>
>> But then you'd still be caching the same things memcached is, so
>> unless you have a lot more ram you'll presumably miss the same rows
>> too.
>>
>> The only 2-layer approach that makes sense to me would be to have
>> cassandra keys cache at 100% behind memcached for the actual rows,
>> which will actually reduce the penalty for a memcache miss by
>> half-ish.
>>
>> On Wed, Mar 31, 2010 at 1:32 PM, David Strauss <david@fourkitchens.com>
>> wrote:
>> > Or, if faking memcached misses is too high a price to pay, queue some
>> > proportion of the reads to replay asynchronously against Cassandra.
>> >
>> > On Wed, 2010-03-31 at 11:04 -0500, Jonathan Ellis wrote:
>> >> Can you redirect some of the reads from memcache to cassandra?  Sounds
>> >> like the cache isn't getting warmed up.
>> >>
>> >> On Wed, Mar 31, 2010 at 11:01 AM, James Golick <jamesgolick@gmail.com>
>> >> wrote:
>> >> > I'm testing on the live cluster, but most of the production reads are
>> >> > being
>> >> > served by the cache. It's definitely the right CF.
>> >> >
>> >> > On Wed, Mar 31, 2010 at 8:30 AM, Jonathan Ellis <jbellis@gmail.com>
>> >> > wrote:
>> >> >>
>> >> >> On Wed, Mar 31, 2010 at 12:01 AM, James Golick
>> >> >> <jamesgolick@gmail.com>
>> >> >> wrote:
>> >> >> > Okay, so now my row cache hit rate jumps between 1.0, 99.5,
95.6,
>> >> >> > and
>> >> >> > NaN.
>> >> >> > Seems like that stat is a little broken.
>> >> >>
>> >> >> Sounds like you aren't getting enough requests for the
>> >> >> getRecentHitRate to make sense.  use getHits / getRequests.
>> >> >>
>> >> >> But if you aren't getting enough requests for getRecentHitRate,
are
>> >> >> you sure you're tuning the cache on the right CF for your 35ms
test?
>> >> >> Are you testing live?  If not, what's your methodology here?
>> >> >>
>> >> >> -Jonathan
>> >> >
>> >> >
>> >
>> >
>> >
>> >
>
>

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