| From: | "Florian G(dot) Pflug" <fgp(at)phlo(dot)org> |
|---|---|
| To: | Hannu Krosing <hannu(at)skype(dot)net> |
| Cc: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jeff Davis <pgsql(at)j-davis(dot)com>, Luke Lonergan <llonergan(at)greenplum(dot)com>, pgsql-hackers(at)postgresql(dot)org, Eng <eng(at)intranet(dot)greenplum(dot)com> |
| Subject: | Re: old synchronized scan patch |
| Date: | 2006-12-05 14:54:20 |
| Message-ID: | 4575881C.60206@phlo.org |
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| Lists: | pgsql-hackers |
Hannu Krosing wrote:
> The worst that can happen, is a hash collision, in which case you lose
> the benefits of sync scans, but you wont degrade compared to non-sync
> scans
But it could cause "mysterious" performance regressions, no?
Image that your app includes two large tables, which are both
scannen frequently. Suppose that synchronous scanning gives this
use-case a noticeable performance boost. Now, you dump and reload
your schema, and suddently the hashes of oids of those tables
collide. You percieve a noticeable drop in performance that you
can neither explain nor fix without a rather deep understanding
of postgres internals.
greetings, Florian Pflug
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