| From: | "Zeugswetter Andreas ADI SD" <Andreas(dot)Zeugswetter(at)s-itsolutions(dot)at> |
|---|---|
| To: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Simon Riggs" <simon(at)2ndquadrant(dot)com> |
| Cc: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Neil Conway" <neilc(at)samurai(dot)com>, "Gregory Stark" <stark(at)enterprisedb(dot)com>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, <pgsql-hackers(at)postgreSQL(dot)org> |
| Subject: | Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable |
| Date: | 2008-01-29 09:40:40 |
| Message-ID: | E1539E0ED7043848906A8FF995BDA57902C23E73@m0143.s-mxs.net |
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| Lists: | pgsql-hackers pgsql-patches |
> It's a good point that we don't want pg_dump to screw up the cluster
> order, but that's the only use case I've seen this far for disabling
> sync scans. Even that wouldn't matter much if our estimate for
> "clusteredness" didn't get screwed up by a table that looks
> like this:
> "5 6 7 8 9 1 2 3 4"
I do think the guc to turn it off is useful, only I don't understand the
reasoning that pg_dump needs it to maintain the basic clustered
property.
Sorry, but I don't grok this at all.
Why the heck would we care if we have 2 parts of the table perfectly
clustered,
because we started in the middle ? Surely our stats collector should
recognize
such a table as perfectly clustered. Does it not ? We are talking about
one
breakage in the readahead logic here, this should only bring the
clustered property
from 100% to some 99.99% depending on table size vs readahead window.
Andreas
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