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HDFS, mail # user - Re: Strange machine behavior


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Re: Strange machine behavior
Robert Dyer 2012-12-11, 03:33
On Sun, Dec 9, 2012 at 5:45 AM, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:

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

I have just done this for that machine.  So far, I have not seen a
re-occurrence of the strange behavior; it appears this might have solved
the problem.
> 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.
>
> Thanks
> ac
>
> 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>
>
>
--

Robert Dyer
[EMAIL PROTECTED]
+
Andy Isaacson 2012-12-10, 19:23
+
Robert Dyer 2012-12-11, 03:30
+
Bharath Mundlapudi 2012-12-11, 02:06
+
Robert Dyer 2012-12-11, 03:32