From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Palle Girgensohn <girgen(at)pingpong(dot)net> |
Cc: | John Hansen <john(at)geeknet(dot)com(dot)au>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Bug? 8.0 does not use partial index |
Date: | 2005-01-14 01:27:21 |
Message-ID: | 18570.1105666041@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Palle Girgensohn <girgen(at)pingpong(dot)net> writes:
> Interesting. Yes, I might be that desperate, actually. As desperate as 30 s
> vs 30 ms can get me... :)
> And this one would actually accumulate stats alright? Looks kinda hairy to
> me. It's not really a partial index anymore, but I guess that doesn't
> matter...
Yeah, it would. The trick is finding a mapping function that will map
all the cases you care about to distinct values.
> How is the behaviour on 7.4 for this stuff? It seems 7.4 does use the
> partial index, but not always, as shown in a previous mail. Will this
> example work on both versions, or just for 8.0?
7.4 doesn't keep stats on functional indexes, so the hack is a
nonstarter there.
I am not sure why you are seeing different results on 7.4 than 8.0 for
the original example --- 7.4 is certainly not smarter than 8.0, and we
seem to have ruled out the idea that some sort of glitch is confusing
the 8.0 planner.
regards, tom lane
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