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From Sambit Tripathy <sambi...@gmail.com>
Subject Re: multi-threaded HTablePool, incrementColumnValue, compaction and large data set
Date Thu, 09 Aug 2012 11:00:27 GMT
So did you get any success with the problem? Well, I think you can try
using it with Asynchbase, a hbase client used in OpenTSDB.

On Mon, Jan 16, 2012 at 6:46 AM, Neil Yalowitz <neilyalowitz@gmail.com>wrote:

> I'm seeing something unusual here and I wanted to see if it has occurred
> for any other HBase 0.90 users.  I've read several emails here that
> recommend NOT using multi-threading in an MR job, so that's certainly under
> consideration.  If anyone could add to their experiences with
> multi-threading in an MR job it would be very helpful.  We are testing both
> implementations (with threading and without), but the threaded solution is
> causing the problem.
> We are processing log files with PUTs in the Map and a followup
> incrementColumnValue() to a separate "counts" table in the Reducer.  The
> reduce phase uses multi-threading.  The Reducer initializes an HTablePool
> in the setup(), starts threads in the reduce() (to a
> Java BlockingQueue/CompletionService) which do the incrementColumnValue()
> and depending on the value returned create a PUT in the "counter" table,
> and in the cleanup() performs a completionService.take() which is ignored
> and flushes the PUTs queued by the threads.
> There are no issues for approximately the first 100GB of data inserted.
>  After approximately 100GB however, every subsequent job has a freeze
> during the Reduce phase.  What I see happening is at some point the Reduce
> (where the incrementColumnValue() takes place) tasks are "hung" and
> eventually killed with reason: task client has not responded for 600
> seconds.  The counters in the reduce job seem to grow briefly but then all
> the tasks' counter stop increasing and the task is eventually killed.
> Oddly, the problem does not occur if compaction is completely disabled (not
> just major, but also setting hbase.hstore.compactionThreshold = 9999999
> and hbase.hstore.blockingStoreFiles = 9999999).
> Could there be a bug with HTablePool for large datasets and compaction?
>  Again, this works as expected for approximately the first 100 jobs (1GB
> each) but consistently fails after that.  Also to repeat, the problem does
> not occur with ALL compaction disabled.
> Difficult problem to describe, but I'm hoping someone may have some
> feedback and/or similar experiences.  I can provide code examples if anyone
> is curious.
> Neil Yalowitz

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