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From Stack <st...@duboce.net>
Subject Re: 0.90 latency performance, cdh3b4
Date Wed, 20 Apr 2011 16:55:48 GMT
On Wed, Apr 20, 2011 at 9:49 AM, Dmitriy Lyubimov <dlieu.7@gmail.com> wrote:
> Ok. Let me ask a question.
> When scan is performed and it obviously covers several regions, are
> scan performance calls done in sinchronous succession or they are done
> in parallel?

The former.

> Assuming scan is returning 40 results but for some weird reason it
> goes to 6 regions and caching is set to 100 (so it can take all of
> them) are individual region request latencies summed or it would be
> max(region request latency)?


The 40 rows are not contiguous in the same region?  If not, the cost
of client setting up new scanner against next region will be inline w/
your read timing (at least an rpc per region).


> Thank you very much.
> -D
> On Tue, Apr 19, 2011 at 6:28 PM, Ted Dunning <tdunning@maprtech.com> wrote:
>> For a tiny test like this, everything should be in memory and latency
>> should be very low.
>> On Tue, Apr 19, 2011 at 5:39 PM, Dmitriy Lyubimov <dlieu.7@gmail.com> wrote:
>>> PS so what should latency be for reads in 0.90, assuming moderate thruput?
>>> On Tue, Apr 19, 2011 at 5:39 PM, Dmitriy Lyubimov <dlieu.7@gmail.com> wrote:
>>>> for this test, there's just no more than 40 rows in every given table.
>>>> This is just a laugh check.
>>>> so i think it's safe to assume it all goes to same region server.
>>>> But latency would not depend on which server call is going to, would
>>>> it? Only throughput would, assuming we are not overloading.
>>>> And we clearly are not as my single-node local version runs quite ok
>>>> response times with the same throughput.
>>>> It's something with either client connections or network latency or
>>>> ... i don't know what it is. I did not set up the cluster but i gotta
>>>> troubleshoot it now :)
>>>> On Tue, Apr 19, 2011 at 5:23 PM, Ted Dunning <tdunning@maprtech.com>
>>>>> How many regions?  How are they distributed?
>>>>> Typically it is good to fill the table some what and then drive some
>>>>> splits and balance operations via the shell.  One more split to make
>>>>> the regions be local and you should be good to go.  Make sure you have
>>>>> enough keys in the table to support these splits, of course.
>>>>> Under load, you can look at the hbase home page to see how
>>>>> transactions are spread around your cluster.  Without splits and local
>>>>> region files, you aren't going to see what you want in terms of
>>>>> performance.

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