2018-01-31 14:15 GMT+01:00 Vitaliy Garnashevich <vgarnashev...@gmail.com>:
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> I've tried to re-run the test for some specific values of > effective_io_concurrency. The results were the same. > > That's why I don't think the order of tests or variability in "hardware" > performance affected the results. > AWS uses some intelligent throttling, so it can be related to hardware. > Regards, > Vitaliy > > > On 31/01/2018 15:01, Rick Otten wrote: > > We moved our stuff out of AWS a little over a year ago because the > performance was crazy inconsistent and unpredictable. I think they do a > lot of oversubscribing so you get strange sawtooth performance patterns > depending on who else is sharing your infrastructure and what they are > doing at the time. > > The same unit of work would take 20 minutes each for several hours, and > then take 2 1/2 hours each for a day, and then back to 20 minutes, and > sometimes anywhere in between for hours or days at a stretch. I could > never tell the business when the processing would be done, which made it > hard for them to set expectations with customers, promise deliverables, or > manage the business. Smaller nodes seemed to be worse than larger nodes, I > only have theories as to why. I never got good support from AWS to help me > figure out what was happening. > > My first thought is to run the same test on different days of the week and > different times of day to see if the numbers change radically. Maybe spin > up a node in another data center and availability zone and try the test > there too. > > My real suggestion is to move to Google Cloud or Rackspace or Digital > Ocean or somewhere other than AWS. (We moved to Google Cloud and have > been very happy there. The performance is much more consistent, the > management UI is more intuitive, AND the cost for equivalent infrastructure > is lower too.) > > > On Wed, Jan 31, 2018 at 7:03 AM, Vitaliy Garnashevich < > vgarnashev...@gmail.com> wrote: > >> Hi, >> >> I've tried to run a benchmark, similar to this one: >> >> https://www.postgresql.org/message-id/flat/CAHyXU0yiVvfQAnR9 >> cyH%3DHWh1WbLRsioe%3DmzRJTHwtr%3D2azsTdQ%40mail.gmail.com# >> CAHyXU0yiVvfQAnR9cyH=HWh1WbLRsioe=mzRJTHwtr=2azs...@mail.gmail.com >> >> CREATE TABLESPACE test OWNER postgres LOCATION '/path/to/ebs'; >> >> pgbench -i -s 1000 --tablespace=test pgbench >> >> echo "" >test.txt >> for i in 0 1 2 4 8 16 32 64 128 256 ; do >> sync; echo 3 > /proc/sys/vm/drop_caches; service postgresql restart >> echo "effective_io_concurrency=$i" >>test.txt >> psql pgbench -c "set effective_io_concurrency=$i; set >> enable_indexscan=off; explain (analyze, buffers) select * from >> pgbench_accounts where aid between 1000 and 10000000 and abalance != 0;" >> >>test.txt >> done >> >> I get the following results: >> >> effective_io_concurrency=0 >> Execution time: 40262.781 ms >> effective_io_concurrency=1 >> Execution time: 98125.987 ms >> effective_io_concurrency=2 >> Execution time: 55343.776 ms >> effective_io_concurrency=4 >> Execution time: 52505.638 ms >> effective_io_concurrency=8 >> Execution time: 54954.024 ms >> effective_io_concurrency=16 >> Execution time: 54346.455 ms >> effective_io_concurrency=32 >> Execution time: 55196.626 ms >> effective_io_concurrency=64 >> Execution time: 55057.956 ms >> effective_io_concurrency=128 >> Execution time: 54963.510 ms >> effective_io_concurrency=256 >> Execution time: 54339.258 ms >> >> The test was using 100 GB gp2 SSD EBS. More detailed query plans are >> attached. >> >> PostgreSQL 9.6.6 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu >> 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609, 64-bit >> >> The results look really confusing to me in two ways. The first one is >> that I've seen recommendations to set effective_io_concurrency=256 (or >> more) on EBS. The other one is that effective_io_concurrency=1 (the worst >> case) is actually the default for PostgreSQL on Linux. >> >> Thoughts? >> >> Regards, >> Vitaliy >> >> > >
