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From Vidhyashankar Venkataraman <vidhy...@yahoo-inc.com>
Subject Re: A possible bug in the scanner.
Date Wed, 13 Apr 2011 14:44:21 GMT
Hi
   We had enabled scanner caching but I don't think it is the same issue because scanner.next
in this case is blocking: the scanner is busy in the region server but hasn't returned anything
yet since a row to be returned hasn't been found yet (all rows have expired but are still
there since they havent been compacted yet).

Vidhya

On 4/13/11 1:44 AM, "Ted Yu" <yuzhihong@gmail.com> wrote:

Have you read the following thread ?
"ScannerTimeoutException when a scan enables caching, no exception when it
doesn't"Did you enable caching ? If not, it is different issue.

On Wed, Apr 13, 2011 at 12:40 AM, Vidhyashankar Venkataraman <
vidhyash@yahoo-inc.com> wrote:

> (This could be a known issue. Please let me know if it is).
>
> We had a set of uncompacted store files in a region. One of the column
> families had a store file of 5 Gigs. The other column families were pretty
> small (a few megabytes at most).
>
>  It so turned out that all these files had rows whose TTL had expired. Now
> when this region was scanned (which should yield a result of a null set), we
> got Scanner timeouts and UnknownScannerExceptions.
>
> And when we tried scanning the region without the large column family, the
> scanner returned back safely with no result.
>
> So, I major compacted it and the scan started working correctly.
>
> So it looks like timeouts happen if the scanner does not return any output
> for a specified time.
> Which isn't exactly the correct thing to do, because it could be the case
> that the scanner was indeed busy but it just so happened that there are no
> rows yet to return back to the client.
>
> We can try increasing the scanner timeout, but this doesn't resolve the
> underlying problem. Is this a know issue?
>
> Thank you
> Vidhya
>


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