Re: old synchronized scan patch - Mailing list pgsql-hackers

From Florian G. Pflug
Subject Re: old synchronized scan patch
Date
Msg-id 4575881C.60206@phlo.org
Whole thread Raw
In response to Re: old synchronized scan patch  (Hannu Krosing <hannu@skype.net>)
Responses Re: old synchronized scan patch
Re: old synchronized scan patch
List 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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