Re: *_collapse_limit, geqo_threshold - Mailing list pgsql-hackers

From Tom Lane
Subject Re: *_collapse_limit, geqo_threshold
Date
Msg-id 19649.1247112389@sss.pgh.pa.us
Whole thread Raw
In response to *_collapse_limit, geqo_threshold  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-hackers
Noah Misch <noah@leadboat.com> writes:
> Describing in those terms illuminates much.  While the concepts do suggest 2^N
> worst-case planning cost, my artificial test case showed a rigid 4^N pattern;
> what could explain that?

Well, the point of the 2^N concept is just that adding one more relation
multiplies the planning work by a constant factor.  It's useful data
that you find the factor to be about 4, but I wouldn't have expected the
model to tell us that.
        regards, tom lane


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