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From Eric Newton <eric.new...@gmail.com>
Subject Re: EXTERNAL: Re: Failing Tablet Servers
Date Fri, 21 Sep 2012 14:32:43 GMT
We regularly send an overwhelming number of small key/value pairs to tablet
servers (see the continuous ingest test).

If your servers are going down with smaller mutations, send the logs again.
 I suspect that the tserver is being pushed into swap, and then the GC is
taking too long.  That causes the tserver to lose its lock in zookeeper.

Make sure that swappiness is set to zero.

-Eric

On Fri, Sep 21, 2012 at 10:12 AM, Cardon, Tejay E
<tejay.e.cardon@lmco.com>wrote:

>  Jim, Eric, and Adam,****
>
> Thanks.  It sounds like you’re all saying the same thing.  Originally I
> was doing each key/value as its own mutation, and it was blowing up much
> faster (probably due to the volume/overhead of the mutation objects
> themselves.  I’ll try refactoring to break them up into something
> in-between.  My keys are small (<25 Bytes), and my values are empty, but
> I’ll aim for ~1,000 key/values per mutation and see how that works out for
> me.****
>
> ** **
>
> Eric,****
>
> I was under the impression that the memory.maps setting was not very
> important when using native maps.  Apparently I’m mistaken there.  What
> does this setting control when in a native map setting?  And, in general,
> what’s the proper balance between tserver_opts and tserver.memory.maps?***
> *
>
> ** **
>
> With regards to the “Finished gathering information from 24 servers in
> 27.45 seconds”  Do you have any recommendations for how to chase down the
> bottleneck?  I’m pretty sure I’m having GC issues, but I’m not sure what is
> causing them on the server side.  I’m sending a fairly small number of very
> large mutation objects, which I’d expect to be a moderate problem for the
> GC, but not a huge one..****
>
> ** **
>
> Thanks again to everyone for being so responsive and helpful.****
>
> ** **
>
> Tejay Cardon****
>
> ** **
>
> ** **
>
> *From:* Eric Newton [mailto:eric.newton@gmail.com]
> *Sent:* Friday, September 21, 2012 8:03 AM
>
> *To:* user@accumulo.apache.org
> *Subject:* EXTERNAL: Re: Failing Tablet Servers****
>
>  ** **
>
> A few items noted from your logs:****
>
> ** **
>
> tserver.memory.maps.max = 1G****
>
>  ** **
>
> If you are giving your processes 10G, you might want to make the map
> larger, say 6G, and then reduce the JVM by 6G.****
>
> ** **
>
> Write-Ahead Log recovery complete for rz<;zw== (8 mutations applied,
> 8000000 entries created)****
>
>  ** **
>
> You are creating rows with 1M columns.  This is ok, but you might want to
> write them out more incrementally.****
>
> ** **
>
> WARN : Running low on memory****
>
>  ** **
>
> That's pretty self-explanatory.  I'm guessing that the very large
> mutations are causing the tablet servers to run out of memory before they
> are held waiting for minor compactions.****
>
> ** **
>
> Finished gathering information from 24 servers in 27.45 seconds****
>
>  ** **
>
> Something is running slow, probably due to GC thrashing.****
>
> ** **
>
> WARN : Lost servers [10.1.24.69:9997[139d46130344b98]]****
>
>  ** **
>
> And there's a server crashing, probably due to an OOM condition.****
>
> ** **
>
> Send smaller mutations.  Maybe keep it to 200K column updates.  You can
> still have 1M wide rows, just send 5 mutations.****
>
> ** **
>
> -Eric****
>
> ** **
>
> On Thu, Sep 20, 2012 at 5:05 PM, Cardon, Tejay E <tejay.e.cardon@lmco.com>
> wrote:****
>
> I’m seeing some strange behavior on a moderate (30 node) cluster.  I’ve
> got 27 tablet servers on large dell servers with 30GB of memory each.  I’ve
> set the TServer_OPTS to give them each 10G of memory.  I’m running an
> ingest process that uses AccumuloInputFormat in a MapReduce job to write
> 1,000 rows with each row containing ~1,000,000 columns in 160,000
> families.  The MapReduce initially runs quite quickly and I can see the
> ingest rate peak on the  monitor page.  However, after about 30 seconds of
> high ingest, the ingest falls to 0.  It then stalls out and my map task are
> eventually killed.  In the end, the map/reduce fails and I usually end up
> with between 3 and 7 of my Tservers dead.****
>
>  ****
>
> Inspecting the tserver.err logs shows nothing, even on the nodes that
> fail.  The tserver.out log shows a java OutOfMemoryError, and nothing
> else.  I’ve included a zip with the logs from one of the failed tservers
> and a second one with the logs from the master.  Other than the out of
> memory, I’m not seeing anything that stands out to me.****
>
>  ****
>
> If I reduce the data size to only 100,000 columns, rather than 1,000,000,
> the process takes about 4 minutes and completes without incident.****
>
>  ****
>
> Am I just ingesting too quickly?****
>
>  ****
>
> Thanks,****
>
> Tejay Cardon****
>
> ** **
>

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