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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Read Performance
Date Wed, 31 Mar 2010 23:15:31 GMT
What does the CFS mbean think read latencies are?  Possibly something
else is introducing latency after the read.

On Wed, Mar 31, 2010 at 5:37 PM, James Golick <jamesgolick@gmail.com> wrote:
> Standard CF. 10 columns per row. Between about 800 bytes and 2k total per
> row.
> On Wed, Mar 31, 2010 at 3:06 PM, Chris Goffinet <goffinet@digg.com> wrote:
>>
>> How many columns in each row?
>> -Chris
>> On Mar 31, 2010, at 2:54 PM, James Golick 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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