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Hadoop, mail # user - Strange machine behavior

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Re: Strange machine behavior
ac@...) 2012-12-09, 11:45

I always set  "vm.swappiness = 0" for my hadoop servers (PostgreSQL servers too).  

The reason is that Linux moves memory pages to swap space if they have not been accessed for a period of time (swapping).  Java virtual machine (JVM) does not act well in the case of swapping that will make MapReduce (and HBase and ZooKeeper) run into trouble.   So I would suggest to set  vm.swappiness = 0.


On 9 Dec 2012, at 12:58 PM, seth wrote:

> 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 <[EMAIL PROTECTED]> 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>