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From "Mesika, Asaf" <asaf.mes...@gmail.com>
Subject Custom preCompact RegionObserver crashes entire cluster on OOME: Heap Space
Date Tue, 12 Feb 2013 05:46:53 GMT
Hi,

I wrote a RegionObserver which does preCompact.
I activated in pre-production, and then entire cluster dropped dead: One RegionServer after
another crashed on OutOfMemoryException: Heap Space.

My preCompact method generates a KeyValue per each set of Column Qualifiers it sees.
When I remove the coprocessor and restart the cluster, cluster remains stable.
I have 8 RS, each has 4 GB Heap. There about 9 regions (from a specific table I'm working
on) per Region Server. 
Running HBase 0.94.3

The crash occur when the major compaction fires up, apparently cluster wide.


My question is this: Where do the KV generated during the compaction process queue up before
being written to the disk? Is this buffer configurable? 
When I wrote the Region Observer my assumption was the the compaction process works in Streaming
fashion, thus even if I decide to generate a KV per KV I see, it still shouldn't be a problem
memory wise.

Of course I'm trying to improve my code so it will generate much less new KV (by simply altering
the existing KVs received from the InternalScanner).

Thank you,

Asaf
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