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From Andrew Purtell <apurt...@apache.org>
Subject Re: Story of my HBase Bugs / Feature Suggestions
Date Sat, 22 Aug 2009 13:59:42 GMT

Cool. I suspected as much. I'm really glad to see those bugs were found and fixed... 

   - Andy

From: Jonathan Gray <jlist@streamy.com>
To: hbase-user@hadoop.apache.org
Sent: Saturday, August 22, 2009 12:24:51 AM
Subject: Re: Story of my HBase Bugs / Feature Suggestions


Bradford ran his imports when there was both a Scanner bug related to snapshotting that opened
up a race condition, as well as the nasty bugs in getClosestBefore used to look things up
in META.

It was most likely a combination of both of these things making for some rather nasty behavior.


Andrew Purtell wrote:
> There are plans to host live region assignments in ZK and keep only an up-to-date copy
of this state in META for use on cold boot. This is on the roadmap for 0.21 but perhaps could
be considered for 0.20.1 also. This may help here. 
> A TM development group saw the same behavior on a 0.19 cluster. We
> postponed looking at this because 0.20 has a significant rewrite of
> region assignment. However, it is interesting to hear such a similar
> description. I worry the underlying cause may be scanners getting stale data on the RS
as opposed to some master problem which could be solved by the above, a more pervasive problem.
Bradford, any chance you kept around logs or similar which may provide clues?
>    - Andy
> ________________________________
> From: Bradford Stephens <bradfordstephens@gmail.com>
> To: hbase-user@hadoop.apache.org
> Sent: Friday, August 21, 2009 6:48:17 AM
> Subject: Story of my HBase Bugs / Feature Suggestions
> Hey there,
> I'm sending out this summary of how I diagnosed what was wrong with my
> cluster in hopes that you can glean some knowledge/suggestions from it :)
> Thanks for the diagnostic footwork.
> A few days ago,  I noticed that simple MR jobs I was running against .20-RC2
> were failing. Scanners were reaching the end of a region, and then simply
> freezing. The only indication I had of this was the Mapper timing out after
> 1000 seconds -- there were no error messages in the logs for either Hadoop
> or HBase.
> It turns out that my table was corrupt:
> 1. Doing a 'GET' from the shell on a row near the end of a region resulted
> in an error: "Row not in expected region", or something to that effect. It
> re-appeared several times, and I never got the row content.
> 2. What the Master UI indicated for the region distribution was totally
> different from what the RS reported. Row key ranges were on different
> servers than the UI knew about, and the nodes reported different start and
> end keys for a region than the UI.
> I'm not sure how this arose: I noticed after a heavy insert job that when we
> tried to shut down our cluster, it took 30 dots and more -- so we manually
> killed master. Would that lead to corruption?
> I finally resolved the problem by dropping the table and re-loading the data
> A few suggestions going forward:
> 1. More useful scanner error messages: GET reported that there was a problem
> finding a certain row, why couldn't Scanner? There wasn't even a timeout or
> anything -- it just sat there.
> 2. A fsck / restore would be useful for HBase. I imagine you can recreate
> .META. using .regioninfo and scanning blocks out of HDFS. This would play
> nice with the HBase bulk loader story, I suppose.
> I'll be happy to work on these in my spare time, if I ever get any ;)
> Cheers,
> Bradford

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