Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable - Mailing list pgsql-hackers

From Zeugswetter Andreas ADI SD
Subject Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable
Date
Msg-id E1539E0ED7043848906A8FF995BDA57902C23FC1@m0143.s-mxs.net
Whole thread Raw
In response to Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable  ("Guillaume Smet" <guillaume.smet@gmail.com>)
Responses Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable
Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable
Re: [PATCHES] Proposed patch: synchronized_scanning GUCvariable
List pgsql-hackers
> > The plural seems better to me; there's no such thing as a solitary
> > synchronized scan, no?  The whole point of the feature is to affect
> > the behavior of multiple scans.
>
> +1. The plural is important IMHO.

ok, good.

> As I stated earlier, I don't really like this argument (we already
> broke badly designed applications a few times in the past) but we
> really need a way to guarantee that the execution of a query is stable
> and doesn't depend on external factors. And the original problem was
> to guarantee that pg_dump builds a dump as identical as possible to
> the existing data by ignoring external factors. It's now the case with
> your patch.
> The fact that it allows us not to break existing applications relying
> too much on physical ordering is a nice side effect though :).

One more question. It would be possible that a session that turned off
the synchronized_seqscans still be a pack leader for other later
sessions.
Do/should we consider that ?

The procedure would be:
start from page 0
iff no other pack is present fill the current scan position for others

Andreas


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