| From: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Fabrízio Mello <fabriziomello(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Parallel Seq Scan |
| Date: | 2015-07-01 20:17:27 |
| Message-ID: | 55944AD7.7020003@archidevsys.co.nz |
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| Lists: | pgsql-hackers |
On 01/07/15 17:37, Amit Kapila wrote:
> On Tue, Jun 30, 2015 at 4:00 AM, Jeff Davis <pgsql(at)j-davis(dot)com
> <mailto:pgsql(at)j-davis(dot)com>> wrote:
> >
> > [Jumping in without catching up on entire thread.
>
[...]
> .
>
> > 2. Where is the speedup coming from? How much of it is CPU and IO
> > overlapping (i.e. not leaving disk or CPU idle while the other is
> > working), and how much from the CPU parallelism? I know this is
> > difficult to answer rigorously, but it would be nice to have some
> > breakdown even if for a specific machine.
> >
>
> Yes, you are right and we have done quite some testing (on the hardware
> available) with this patch (with different approaches) to see how much
> difference it creates for IO and CPU, with respect to IO we have found
> that it doesn't help much [1], though it helps when the data is cached
> and there are really good benefits in terms of CPU [2].
>
[...]
I assume your answer refers to a table on one spindle of spinning rust.
QUESTIONS:
1. what about I/O using an SSD?
2. what if the table is in a RAID array (of various types), would
having the table spread over multiple spindles help?
Cheers,
Gavin
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