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From Jean-Marc Spaggiari <jean-m...@spaggiari.org>
Subject Re: Compactions nice to have features
Date Thu, 09 Oct 2014 13:31:46 GMT
For #4, one more thing me might want to add is a safety valve to increase
throttle in case compaction queue become bigger than a certain value?

JM

2014-10-09 1:20 GMT-04:00 lars hofhansl <larsh@apache.org>:

> Hi Michael,
>
> your math is right.
>
>
> I think the issue is that it actually is easy to max out the ToR switch
> (and hence starve out other traffic), so we might want to protect the ToR
> switch from prolonged heavy compaction traffic in order to keep some of the
> bandwidth free for other traffic.
> Vladimir issues were around slowing other traffic while compactions are
> running.
>
>
> -- Lars
>
>
>
> ----- Original Message -----
> From: Michael Segel <michael_segel@hotmail.com>
> To: dev@hbase.apache.org; lars hofhansl <larsh@apache.org>
> Cc: Vladimir Rodionov <vladrodionov@gmail.com>
> Sent: Wednesday, October 8, 2014 12:30 PM
> Subject: Re: Compactions nice to have features
>
>
>
> On Oct 5, 2014, at 11:01 PM, lars hofhansl <larsh@apache.org> wrote:
>
> >>> - rack IO throttle. We should add that to accommodate for over
> subscription at the ToR level.
> >> Can you decipher that, Lars?
> >
> > ToR is "Top of Rack" switch. Over subscription means that a ToR switch
> usually does not have enough bandwidth to serve traffic in and out of rack
> at full speed.
> > For example if you had 40 machines in a rack with 1ge links each, and
> the ToR switch has a 10ge uplink, you'd say the ToR switch is 4 to 1 over
> subsctribed.
> >
> >
> > Was just trying to say: "Yeah, we need that" :)
> >
>
>
> Hmmm.
>
> Rough math…  using 3.5” SATA II (7200 RPM) drives … 4 drives would max out
> 1GbE.  So then  a server with 12 drives would max out 3Gb/S. Assuming 3.5”
> drives. 2.5” drives and SATAIII would push this up.
> So in theory you could get 5Gb/S or more from a node.
>
> 16 serves per rack… (again YMMV based on power, heat, etc … ) thats 48Gb/S
> and up.
>
> If you had 20 servers and they had smaller (2.5” drives) 5Gb/S x 20 =
> 100Gb/S.
>
> So what’s the width of the fabric?  (YMMV based on ToR)
>
> I don’t know why you’d want to ‘throttle’ because the limits of the ToR
> would throttle you already.
>
> Of course I’m assuming that you’re running a M/R job that’s going full
> bore.
>
>
> Are you seeing this?
> I would imagine that you’d have a long running job maxing out the I/O and
> seeing a jump in wait CPU over time.
>
> And what’s the core to spindle ratio?
>

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