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HBase >> mail # user >> Memory Consumption and Processing questions


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Re: Memory Consumption and Processing questions
Makes me wonder if high speed interconnects and little to no block cache
would work better--basically rely on each machine to hold the highly used
blocks in os cache and push them around quickly if they are needed
elsewhere.  Of course it's all just a thought experiment at this point.  The
cost of having high speed interconnects would probably be substantially more
than provisioning extra memory to hold cached blocks twice.  There is also
the thought that if the blocks are cached by Hbase, they would appear rarely
used from the os standpoint and are, therefore, unlikely to be in cache.
On Mon, Aug 2, 2010 at 8:39 AM, Edward Capriolo <[EMAIL PROTECTED]>wrote:

> On Mon, Aug 2, 2010 at 11:33 AM, Jacques <[EMAIL PROTECTED]> wrote:
> > You're right, of course.  I shouldn't generalize too much.  I'm more
> trying
> > to understand the landscape than pinpoint anything specific.
> >
> > Quick question: since the block cache is unaware of the location of
> files,
> > wouldn't it overlap the os cache for hfiles once they are localized after
> > compaction?  Any guidance on how to tune the two?
> >
> > thanks,
> > Jacques
> >
> > On Sun, Aug 1, 2010 at 9:08 PM, Jonathan Gray <[EMAIL PROTECTED]>
> wrote:
> >
> >> One reason not to extrapolate that is that leaving lots of memory for
> the
> >> linux buffer cache is a good way to improve overall performance of
> typically
> >> i/o bound applications like Hadoop and HBase.
> >>
> >> Also, I'm unsure that "most people use ~8 for hdfs/mr".  DataNodes
> >> generally require almost no significant memory (though generally run
> with
> >> 1GB); their performance will improve with more free memory for the os
> buffer
> >> cache.  As for MR, this completely depends on the tasks running.  The
> >> TaskTrackers also don't require significant memory, so this completely
> >> depends on the number of tasks per node and the memory requirements of
> the
> >> tasks.
> >>
> >> Unfortunately you can't always generalize the requirements too much,
> >> especially in MR.
> >>
> >> JG
> >>
> >> > -----Original Message-----
> >> > From: Jacques [mailto:[EMAIL PROTECTED]]
> >> > Sent: Sunday, August 01, 2010 5:30 PM
> >> > To: [EMAIL PROTECTED]
> >> > Subject: Re: Memory Consumption and Processing questions
> >> >
> >> > Thanks, that was very helpful.
> >> >
> >> > Regarding 24gb-- I saw people using servers with 32gb of server memory
> >> > (a
> >> > recent thread here and hstack.org).  I extrapolated the use since it
> >> > seems
> >> > most people use ~8 for hdfs/mr.
> >> >
> >> > -Jacques
> >> >
> >> >
> >> > On Sun, Aug 1, 2010 at 11:39 AM, Jonathan Gray <[EMAIL PROTECTED]>
> >> > wrote:
> >> >
> >> > >
> >> > >
> >> > > > -----Original Message-----
> >> > > > From: Jacques [mailto:[EMAIL PROTECTED]]
> >> > > > Sent: Friday, July 30, 2010 1:16 PM
> >> > > > To: [EMAIL PROTECTED]
> >> > > > Subject: Memory Consumption and Processing questions
> >> > > >
> >> > > > Hello all,
> >> > > >
> >> > > > I'm planning an hbase implementation and had some questions I was
> >> > > > hoping
> >> > > > someone could help with.
> >> > > >
> >> > > > 1. Can someone give me a basic overview of how memory is used in
> >> > Hbase?
> >> > > >  Various places on the web people state that 16-24gb is the
> minimum
> >> > for
> >> > > > region servers if they also operate as hdfs/mr nodes.  Assuming
> >> > that
> >> > > > hdfs/mr
> >> > > > nodes consume ~8gb that leaves a "minimum" of 8-16gb for hbase.
>  It
> >> > > > seems
> >> > > > like lots of people suggesting use of even 24gb+ for hbase.  Why
> so
> >> > > > much?
> >> > > >  Is it simply to avoid gc problems?  Have data in memory for fast
> >> > > > random
> >> > > > reads? Or?
> >> > >
> >> > > Where exactly are you reading this from?  I'm not actually aware of
> >> > people
> >> > > using 24GB+ heaps for HBase.
> >> > >
> >> > > I would not recommend using less than 4GB for RegionServers.  Beyond
> >> > that,
> >> > > it very much depends on your application.  8GB is often sufficient