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HBase >> mail # user >> Poor HBase map-reduce scan performance

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Re: Poor HBase map-reduce scan performance
I tweaked Enis's snapshot input format and backported it to 0.94.6 and have snapshot scanning functional on my system. Performance is dramatically better, as expected i suppose. I'm seeing about 3.6x faster performance vs TableInputFormat. Also, HBase doesn't get bogged down during a scan as the regionserver is being bypassed. I'm very excited by this. There are some issues with file permissions and library dependencies but nothing that can't be worked out.

On Jun 5, 2013, at 6:03 PM, lars hofhansl <[EMAIL PROTECTED]> wrote:

> That's exactly the kind of pre-fetching I was investigating a bit ago (made a patch, but ran out of time).
> This pre-fetching is strictly client only, where the client keeps the server busy while it is processing the previous batch, but filling up a 2nd buffer.
> -- Lars
> ________________________________
> From: Sandy Pratt <[EMAIL PROTECTED]>
> Sent: Wednesday, June 5, 2013 10:58 AM
> Subject: Re: Poor HBase map-reduce scan performance
> Yong,
> As a thought experiment, imagine how it impacts the throughput of TCP to
> keep the window size at 1.  That means there's only one packet in flight
> at a time, and total throughput is a fraction of what it could be.
> That's effectively what happens with RPC.  The server sends a batch, then
> does nothing while it waits for the client to ask for more.  During that
> time, the pipe between them is empty.  Increasing the batch size can help
> a bit, in essence creating a really huge packet, but the problem remains.
> There will always be stalls in the pipe.
> What you want is for the window size to be large enough that the pipe is
> saturated.  A streaming API accomplishes that by stuffing data down the
> network pipe as quickly as possible.
> Sandy
> On 6/5/13 7:55 AM, "yonghu" <[EMAIL PROTECTED]> wrote:
>> Can anyone explain why client + rpc + server will decrease the performance
>> of scanning? I mean the Regionserver and Tasktracker are the same node
>> when
>> you use MapReduce to scan the HBase table. So, in my understanding, there
>> will be no rpc cost.
>> Thanks!
>> Yong
>> On Wed, Jun 5, 2013 at 10:09 AM, Sandy Pratt <[EMAIL PROTECTED]> wrote:
>>> https://issues.apache.org/jira/browse/HBASE-8691
>>> On 6/4/13 6:11 PM, "Sandy Pratt" <[EMAIL PROTECTED]> wrote:
>>>> Haven't had a chance to write a JIRA yet, but I thought I'd pop in here
>>>> with an update in the meantime.
>>>> I tried a number of different approaches to eliminate latency and
>>>> "bubbles" in the scan pipeline, and eventually arrived at adding a
>>>> streaming scan API to the region server, along with refactoring the
>>> scan
>>>> interface into an event-drive message receiver interface.  In so
>>> doing, I
>>>> was able to take scan speed on my cluster from 59,537 records/sec with
>>> the
>>>> classic scanner to 222,703 records per second with my new scan API.
>>>> Needless to say, I'm pleased ;)
>>>> More details forthcoming when I get a chance.
>>>> Thanks,
>>>> Sandy
>>>> On 5/23/13 3:47 PM, "Ted Yu" <[EMAIL PROTECTED]> wrote:
>>>>> Thanks for the update, Sandy.
>>>>> If you can open a JIRA and attach your producer / consumer scanner
>>> there,
>>>>> that would be great.
>>>>> On Thu, May 23, 2013 at 3:42 PM, Sandy Pratt <[EMAIL PROTECTED]>
>>> wrote:
>>>>>> I wrote myself a Scanner wrapper that uses a producer/consumer
>>> queue to
>>>>>> keep the client fed with a full buffer as much as possible.  When
>>>>>> scanning
>>>>>> my table with scanner caching at 100 records, I see about a 24%
>>> uplift
>>>>>> in
>>>>>> performance (~35k records/sec with the ClientScanner and ~44k
>>>>>> records/sec
>>>>>> with my P/C scanner).  However, when I set scanner caching to 5000,
>>>>>> it's
>>>>>> more of a wash compared to the standard ClientScanner: ~53k
>>> records/sec
>>>>>> with the ClientScanner and ~60k records/sec with the P/C scanner.