You probably made it less likely that your scanners will scan the same HFile in parallel.
From: Eugeny Morozov <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]; lars hofhansl <[EMAIL PROTECTED]>
Sent: Thursday, December 20, 2012 2:32 AM
Subject: Re: Many scanner opening
Cool stuff! Thanks a lot! I'm not sure I can apply the patch, cause we're
using CDH-4.1.1, but increasing size of internal scanner does the trick -
decreased number of scanners.
At least temporarily it's good enough.
On Wed, Dec 19, 2012 at 6:23 AM, lars hofhansl <[EMAIL PROTECTED]> wrote:
> You might have run into HBASE-7336.
> (Not available in any official release, yet)
> If you're using 0.94 (and probably 0.92) you can just apply this patch
> (it's save and simple).
> From: Eugeny Morozov <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> Sent: Tuesday, December 18, 2012 12:01 AM
> Subject: Many scanner opening
> We faced an issue recently that the more map tasks are completed, the
> longer it takes to complete one more map task.
> In our architecture we have two scanners to read the table. The first one,
> which is called 'outer' scanner is reading table and filter some rowkeys.
> These rowkeys are used as a filter for second scanner - 'internal'. Thus we
> constantly open 'internal' scanner with different filters.
> As an additional symptoms we see that our cluster practically does nothing
> - there is no CPU loading, no disk loading, no network, etc. Most of the
> time it means we are waiting on some locks, but I'm not sure.
> I would appreciate any ideas or suggestions to understand the case.
> Thank you in advance.
> Evgeny Morozov
> Developer Grid Dynamics
> Skype: morozov.evgeny
> [EMAIL PROTECTED]
Developer Grid Dynamics