| From: | Stephen Frost <sfrost(at)snowman(dot)net> |
|---|---|
| To: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> |
| Cc: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Andres Freund <andres(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Relation extension scalability |
| Date: | 2015-04-02 03:14:59 |
| Message-ID: | 20150402031459.GT3663@tamriel.snowman.net |
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| Lists: | pgsql-hackers |
* Amit Langote (Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp) wrote:
> On 02-04-2015 AM 09:24, Jim Nasby wrote:
> > The other potential advantage (and I have to think this could be a BIG
> > advantage) is extending by a large amount makes it more likely you'll get
> > contiguous blocks on the storage. That's going to make a big difference for
> > SeqScan speed. It'd be interesting if someone with access to some real systems
> > could test that. In particular, seqscan of a possibly fragmented table vs one
> > of the same size but created at once. For extra credit, compare to dd bs=8192
> > of a file of the same size as the overall table.
>
> Orthogonal to topic of the thread but this comment made me recall a proposal
> couple years ago[0] to add (posix_)fallocate to mdextend(). Wonder if it helps
> the case?
As I recall, it didn't, and further, modern filesystems are pretty good
about avoiding fragmentation anyway..
I'm not saying Jim's completely off-base with this idea, I'm just not
sure that it'll really buy us much.
Thanks,
Stephen
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