Hi,
I've tried to run a benchmark, similar to this one:
https://www.postgresql.org/message-id/flat/CAHyXU0yiVvfQAnR9cyH%3DHWh1WbLRsioe%3DmzRJTHwtr%3D2azsTdQ%40mail.gmail.com#CAHyXU0yiVvfQAnR9cyH=HWh1WbLRsioe=mzRJTHwtr=2azsTdQ@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
