Isn't the use of NFS pretty high on the "things not to do with
Postgres" list?
On 1/22/19 12:13 AM, Tim Cross wrote:
I suspect the main reason there are no official
recommendations is because setting the IO scheduler is a low
level optimisation, getting very close to a 'mciro-optimisation'
compared to other areas of optimisation. Some even consider
playing at this level to be somewhat of a black art - primarily
because it is very complicated and dependent on many, many
variables (hardware, use profile, data profile etc). For these
reasons, I doubt there is a clear 'winner' for PG (especially as
PG doesn't do direct IO to disk like Oracle does). I suspect
the fact your using NFS will overshadow any differences with the
IO scheduling algorithm as well. Regardless, the only reliable
way to select the best algorithm would be extensive benchmarking
using realistic data and usage profiles.
Thanks Laurenz
Surprise to know that there are no official
recommendation from PostgreSQL.
AB_ba# wrote:
> I searched the complete PostgreSQL Documentation but
didn't get anything with respect to IO scheduler
recommendation.
> What is being recommended by PostgreSQL ?
There is no clear recommendation.
I personally have seen workloads where changing from "cfq"
to "deadline"
or "noop" improved performance by a factor of 4, but on
many systems "cfq"
seems to be doing at least as good as the others.
I believe that it depends a lot on your hardware
configuration and
your workload, and you are best advised to run a realistic
load test.
> Which is the best IO scheduler considering the Data
is hosted on NFS?
No idea - probably depends on what is behind the NFS.
Make sure to use hard, fg mounts.
If you can, use "jumbo frames" so that an 8KB block can
fit into
a single IP frame.
Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com
--
Thanks
and Regards
ANUP BHARTI
--
regards,
Tim
--
Tim Cross
--
Angular momentum makes the world go 'round.
|
