You do have a finite amount of bandwidth per-instance. On c5.xlarge, it is 3500 Mbit/sec, no matter how many iops you buy. Keep an eye on yur overall EBS bandwidth utilization.
On Sun, Mar 17, 2019 at 11:42 AM Gunther <r...@gusw.net> wrote: > On 3/14/2019 11:11, Jeremy Schneider wrote: > > On 3/14/19 07:53, Gunther wrote: > >> 2. build a low level "spreading" scheme which is to take the partial > >> files 4653828 and 4653828.1, .2, _fsm, etc. and move each to > another > >> device and then symlink it back to that directory (I come back to > this!) > > ... > >> To 2. I find that it would be a nice feature of PostgreSQL if we could > >> just use symlinks and a symlink rule, for example, when PostgreSQL finds > >> that 4653828 is in fact a symlink to /otherdisk/PG/16284/4653828, then > >> it would > >> > >> * by default also create 4653828.1 as a symlink and place the actual > >> data file on /otherdisk/PG/16284/4653828.1 > > How about if we could just specify multiple tablespaces for an object, > > and then PostgreSQL would round-robin new segments across the presently > > configured tablespaces? This seems like a simple and elegant solution > > to me. > > Very good idea! I agree. > > Very important also would be to take out the existing patch someone had > contributed to allow toast tables to be assigned to different tablespaces. > > >> 4. maybe I can configure in AWS EBS to reserve more IOPS -- but why > >> would I pay for more IOPS if my cost is by volume size? I can just > >> make another volume? or does AWS play a similar trick on us with > >> IOPS being limited on some "credit" system??? > > Not credits, but if you're using gp2 volumes then pay close attention to > > how burst balance works. A single large volume is the same price as two > > striped volumes at half size -- but the striped volumes will have double > > the burst speed and take twice as long to refill the burst balance. > > Yes, I learned that too. It seems a very interesting "bug" of the Amazon > GP2 IOPS allocation scheme. They say it's like 3 IOPS per GiB, so if I > have 100 GiB I get 300 IOPS. But it also says minimum 100. So that means > if I have 10 volumes of 10 GiB each, I get 1000 IOPS minimum between > them all. But if I have it all on one 100 GiB volume I only get 300 IOPS. > > I wonder if Amazon is aware of this. I hope they are and think that's > just fine. Because I like it. > > It also is a clear sign to me that I want to use page sizes > 4k for the > file system. I have tried on Amazon Linux to use 8k block sizes of the > XFS volume, but I cannot mount those, since the Linux says it can > currently only deal with 4k blocks. This is another reason I consider > switching the database server(s) to FreeBSD. OTOH, who knows may be > this 4k is a limit of the AWS EBS infrastructure. After all, if I am > scraping the 300 or 1000 IOPS limit already and if I can suddenly > upgrade my block sizes per IO, I double my IO throughput. > > regards, > -Gunther > > >
