On 11/08/2011 02:49 PM, Ondrej Ivanič wrote:
Usually CPU is not bottleneck but I it was when I put Pustgres on
FusionIO. The problem is that PG spreads reads too much . iostat
reports very low drive utilisation and very low queue size.
"Spreads reads too much" ?
Are you saying there's too much random I/O? Is it possible it'd benefit
from a column store?
When you're using Greenplum are you using "Polymorphic Data Storage"
column storage "WITH (orientation=column)" ?
Or is the performance different just in better utilisation of the
hardware under Greenplum?
I've played with effective_io_concurrency (went thru entire range: 1,
2, 5, 10, 20, 50, 100, 200, 500, 1000) but nothing improved.
Hm, ok. Scratch that then.
Is there
a way to get PG backed IO stats using stock CentOS (5.7) kernel and
tools? (I can't change my env easily)
Dunno; check postgresql high performance (book), the manual, etc. Useful
tools are the pg_stat_ tables, "vmstat", "iostat", "iotop", etc.
I'm not at all surprised by that. PostgreSQL couldn't use the full resources
of your system when it was expressed as just one query.
This is very interesting area to work in but my lack of C/C++ and PG
internals puts me out of the game :)
That's a cop-out! I say that as someone who _used_ to have no C
knowledge, but learned it to get things done on code I use.
That said, Pg's codebase isn't exactly trivial :S and trying to get
involved in major re-engineering like parallelisation isn't going to be
practical when you're just getting started.
--
Craig Ringer
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