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From "Cardon, Tejay E" <>
Subject RE: EXTERNAL: Re: Failing Tablet Servers
Date Fri, 21 Sep 2012 14:50:10 GMT
Alright.  So I'm changing it to:

1.        moderate size mutations ~1,000 key/values per mutation.

2.       Tserver_opts = 5g

3.       Memory.maps = 3g

4.       Swappiness = 0 (right now I'm at 20)

It sounds like those are all settings I should fix anyway, so we'll do them all.  I'll report
back if that doesn't fix the problem.

Thanks again for all the help

Tejay Cardon
From: Eric Newton []
Sent: Friday, September 21, 2012 8:33 AM
Subject: Re: EXTERNAL: Re: Failing Tablet Servers

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.

On Fri, Sep 21, 2012 at 10:12 AM, Cardon, Tejay E <<>>
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.

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 [<>]
Sent: Friday, September 21, 2012 8:03 AM

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

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 [[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.


On Thu, Sep 20, 2012 at 5:05 PM, Cardon, Tejay E <<>>
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?

Tejay Cardon

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