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From David Van Couvering <da...@vancouvering.com>
Subject HBase and failure notification
Date Thu, 26 Feb 2009 18:17:51 GMT
Hey, all.  I'm doing a bit of a survey of distributed key/value stores out
there.  HBase looks pretty interesting, nice to see an open source version
of BigTable out there.

HBase is obviously clustered, but what I can't figure out is how it does
cluster management.  It looks like you have to configure it to tell it all
the machines that have region servers, and that implies to me that *you*
have to start and manage the region servers - HBase doesn't do any of that
for you.  So I think that means that it doesn't have any node monitoring
support - you have to have your own monitoring system that detects failed
nodes and notifies you and/or restarts them for you.

Also, the architecture document says "if [the master server] detects a
HRegionServer is no longer reachable, it will split the HRegionServer's
write-ahead log so that there is now one write-ahead log for each region
that the HRegionServer was serving. After it has accomplished this, it will
reassign the regions that were being served by the unreachable
HRegionServer"

This seems to imply that even though the HRegionServer is unreachable,
somehow it's write-ahead log and the regions it was serving are.  Perhaps I
don't fully understand HFS, but is this a guarantee when the node hosting
the HRegionServer is down?  What happens if you can't get to the write-ahead
log and/or some of the regions the region server was serving?

Thanks,

David

-- 
David W. Van Couvering

I am looking for a senior position working on server-side Java systems.
 Feel free to contact me if you know of any opportunities.

http://www.linkedin.com/in/davidvc
http://davidvancouvering.blogspot.com
http://twitter.com/dcouvering


-- 
David W. Van Couvering

I am looking for a senior position working on server-side Java systems.
 Feel free to contact me if you know of any opportunities.

http://www.linkedin.com/in/davidvc
http://davidvancouvering.blogspot.com
http://twitter.com/dcouvering

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