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From steven zhuang <steven.zhuang.1...@gmail.com>
Subject Re: multiple scanners on same table will cause problem? Scan results change among different tries.
Date Thu, 22 Apr 2010 12:17:12 GMT
hi, Michael,

               Sorry for not making the question clear, there are multiple
scanners scanning a single table, there might be the case multiple scanners
reading from a single region.
       please see answers inline.

On Thu, Apr 22, 2010 at 8:08 PM, Michael Segel <michael_segel@hotmail.com>wrote:

> I'm sorry, but are you trying to say that you have multiple scanners trying
> to read from a single region and the result sets do not match?
>  Yes, the result sets do not match.

> I guess it would be an easy test, enter a bunch of rows in to a region and
> have a unique integer for each row. (1,2,3,...)
> Then run a bunch of unfiltered scans in parallel, and generate a sum from
> the scan. If any of the sums do not match, then you have a potential issue
> on concurency/row locking, and row isolation level.  How does HBase handle
> row level locking and isolation levels?
> I have iterate on the rows/columnfamilies/cells, and printed the content of
each cell, found that there are some cells missing in some scan result set.

> -Mike
> > Date: Thu, 22 Apr 2010 17:07:47 +0800
> > Subject: multiple scanners on same table will cause problem? Scan results
>     change among different tries.
> > From: steven.zhuang.1984@gmail.com
> > To: hbase-user@hadoop.apache.org
> >
> > hi, All,
> >           Has anybody do scan on one table using multiple scanners at the
> > same time and  found some inconsistent problem?
> >           I am doing query on a table using dozens(20-120) of scanners in
> > parallel(multiple threads), trying to take advantage of the multiple
> cores.
> > But I found the scan results doesn't consist among several goes. I have
> > checked my code, seems there is no bug in it. So I guess the problem may
> > come from the HBase itself.
> >           My HBase version is 0.20.3.
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