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From Kesten Broughton <kbrough...@21ct.com>
Subject ingest problems
Date Tue, 11 Feb 2014 16:10:37 GMT
Hi there,

We have been experimenting with accumulo for about two months now.  Our biggest painpoint
has been on ingest.
Often we will have ingest process fail 2 or 3 times 3/4 of the way through an ingest and then
on a final try it works, without any changes.

Once the ingest works, the cluster is usually stable for querying for weeks or months only
requiring the occasional start-all.sh if there is a problem.

Sometimes our ingest can be 24 hours long, and we need a stronger ingest story to be able
to commit to accumulo.
Our cluster architecture has been:
3 hdfs datanodes overlaid with name node, secondary nn and accumulo master each collocated
with a datanode, and a zookeeper server on each.
We realize this is not optimal and are transitioning to separate hardware for zookeepers and
name/secondary/accumulomaster nodes.
However, the big concern is that sometimes a failed ingest will bork the whole cluster and
we have to re-init accumulo with an accumulo init destroying all our data.
We have experienced this on at least three different clusters of this description.

The most recent attempt was on a 65GB dataset.   The cluster had been up for over 24 hours.
 The ingest test takes 40 mins and about 5 mins in, one of the datanodes failed.
There were no error logs on the failed node, and the two other nodes had logs filled with
zookeeper connection errors.  We were unable to recover the cluster and had to re-init.

I know a vague description of problems is difficult to respond to, and the next time we have
an ingest failure, i will bring specifics forward.  But I’m writing to know if
1.  Ingest failures are a known fail point for accumulo, or if we are perhaps unlucky/mis-configured.
2.  Are there any guidelines for capturing ingest failures / determining root causes when
errors don’t show up in the logs
3.  Are there any means of checkpointing a data ingest, so that if a failure were to occur
at hour 23.5 we could roll back to hour 23 and continue.  Client code could checkpoint and
restart at the last one, but if the underlying accumulo cluster can’t be recovered, that’s
of no use.

thanks,

kesten

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