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From seth <s...@untethered.org>
Subject Re: Strange machine behavior
Date Sun, 09 Dec 2012 04:58:20 GMT
Oracle frequently recommends vm.swappiness = 0 to get well behaved RAC nodes.  Otherwise you
start paging out things you don't usually want paged out in favor of a larger filesystem cache.

There is also a vm parameter that controls the minimum size of the free chain, might want
to increase that a bit.

Also, look into hosting your JVM heap on huge pages, they can't be paged out and will help
the JVM perform better too.

On Dec 8, 2012, at 6:09 PM, Robert Dyer <rdyer@iastate.edu> wrote:

> Has anyone experienced a TaskTracker/DataNode behaving like the attached image?
> This was during a MR job (which runs often).  Note the extremely high System CPU time.
 Upon investigating I saw that out of 64GB ram the system had allocated almost 45GB to cache!
> I did a sudo sh -c "sync ; echo 3 > /proc/sys/vm/drop_cache ; sync" which is roughly
where the graph goes back to normal (much lower System, much higher User).
> This has happened a few times.
> I have tried playing with the sysctl vm.swappiness value (default of 60) by setting it
to 30 (which it was at when the graph was collected) and now to 10.  I am not sure that helps.
> Any ideas?  Anyone else run into this before?
> 24 cores
> 64GB ram
> 4x2TB sata3 hdd
> Running Hadoop 1.0.4, with a DataNode (2gb heap), TaskTracker (2gb heap) on this machine.
> 24 map slots (1gb heap each), no reducers.
> Also running HBase 0.94.2 with a RS (8gb ram) on this machine.
> <cpu-use.png>

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