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From lars hofhansl <la...@apache.org>
Subject Re: independent scans to same region processed serially
Date Sat, 09 Feb 2013 17:02:12 GMT
I looked through the code. Nothing obvious jumps out.
We can sit together on Monday and run it through a profiler.

-- Lars

----- Original Message -----
From: James Taylor <jtaylor@salesforce.com>
To: "user@hbase.apache.org" <user@hbase.apache.org>; lars hofhansl <larsh@apache.org>
Sent: Friday, February 8, 2013 9:52 PM
Subject: Re: independent scans to same region processed serially

All data is the blockcache and there are plenty of handlers. To repro, 
you could:
- create a table pre-split into, for example, three regions
- execute serially a scan on the middle region
- execute two parallel scans each on half of the middle region
- you'd expect the parallel scan to execute near twice as fast, but 
we're seeing it execute slower than the serial scan.
We're using the same HConnection with different HTable instances for 
each scan.


On 02/08/2013 06:51 PM, lars hofhansl wrote:
> Is your data all in the blockcache, otherwise you might have run into HBASE-7336 (https://issues.apache.org/jira/browse/HBASE-7336).Fixed
> I assume you have enough handlers, etc. (i.e. does the same happen if issue multiple
scan request across different region of the same region server?)
> -- Lars
> ________________________________
>   From: James Taylor <jtaylor@salesforce.com>
> To: HBase User <user@hbase.apache.org>
> Sent: Friday, February 8, 2013 5:49 PM
> Subject: independent scans to same region processed serially
> Wanted to check with folks and see if they've seen an issue around this before digging
in deeper. I'm on 0.94.2. If I execute in parallel multiple scans to different parts of the
same region, they appear to be processed serially. It's actually faster from the client side
to execute a single serial scan than it is to execute multiple parallel scans to different
segments of the region. I do have region observer coprocessors for the table I'm scanning,
but my code is not doing any synchronization.
> Is there a known limitation in this area? Anyone else see anything similar?
>      James

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