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 <la...@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_se...@hotmail.com> > To: dev@hbase.apache.org; lars hofhansl <la...@apache.org> > Cc: Vladimir Rodionov <vladrodio...@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 <la...@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? >
