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From Brennon Church <bren...@getjar.com>
Subject Re: Lost regions question
Date Fri, 12 Apr 2013 16:04:14 GMT

We lost the data when the parent regions got reopened.  My guess, and 
it's only that, is that the regions were  essentially empty when they 
started up again in these cases.  We definitely lost data from the tables.

I've looked through the hdfs and hbase logs and can't find any obvious 
difference between a successful split and these failed ones.  All steps 
show up the same in all cases.  After the handled split message that 
listed the parent and daughter regions, the next reference is to the 
parent regions once again as hbase is started back up after the 
failure.  No further reference to the daughters is made.

I couldn't cleanly shut several of the regionservers down, so they were 
abruptly killed, yes.

HBase version is 0.92.0, and hadoop is 1.0.1.



On 4/11/13 10:58 PM, ramkrishna vasudevan wrote:
> When you say that the parent regions got reopened does that mean that you
> did not lose any data(any data could not be read).  The reason am asking is
> if after the parent got split into daughters and the data was written to
> daughters and if the daughters related files could not be opened you could
> have ended up in not able to read the data.
> Some logs could tell us what made the parent to get reopened rather than
> daughters.  Another thing i would like to ask is was the cluster brought
> down abruptly by killing the RS.
> Which version of HBase?
> Regards
> Ram
> On Fri, Apr 12, 2013 at 11:20 AM, Brennon Church <brennon@getjar.com> wrote:
>> Hello,
>> I had an interesting problem come up recently.  We have a few thousand
>> regions across 8 datanode/regionservers.  I made a change, increasing the
>> heap size for hadoop from 128M to 2048M which ended up bringing the cluster
>> to a complete halt after about 1 hour.  I reverted back to 128M and turned
>> things back on again but didn't realize at the time that I came up with 9
>> fewer regions than I started.  Upon further investigation, I found that all
>> 9 missing regions were from splits that occurred while the cluster was
>> running after making the heap change and before it came to a halt.  There
>> was a 10th regions (5 splits involved in total) that managed to get
>> recovered.  The really odd thing is that in the case of the other 9
>> regions, the original parent regions, which as far as I can tell in the
>> logs were deleted, were re-opened upon restarting things once again.  The
>> daughter regions were gone.  Interestingly, I found the orphaned datablocks
>> still intact, and in at least some cases have been able to extract the data
>> from them and will hopefully re-add it to the tables.
>> My question is this.  Does anyone know based on the rather muddled
>> description I've given above, what could have possibly happened here?  My
>> best guess is that the bad state that hdfs was in caused some critical
>> component of the split process to be missed, which resulted a reference to
>> the parent regions sticking around and losing the references to the
>> daughter regions.
>> Thanks for any insight you can provide.
>> --Brennon

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