-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.