| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Christopher Kings-Lynne" <chriskl(at)familyhealth(dot)com(dot)au> |
| Cc: | "Dave Page" <dpage(at)vale-housing(dot)co(dot)uk>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Partial index on date column |
| Date: | 2003-03-07 04:44:15 |
| Message-ID: | 27669.1047012255@sss.pgh.pa.us |
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"Christopher Kings-Lynne" <chriskl(at)familyhealth(dot)com(dot)au> writes:
> Obviously to you and I, referrer=1 implies that referrer is not null, but
> the planner doesn't know that.
Actually the planner does make exactly that deduction in some other
contexts --- but I'm hesitant to expend the cycles for partial indexes.
Partial-index condition matching is a horribly difficult problem in
general, and we only attempt a few limited cases right now. I don't
think we want to put a general-purpose theorem prover in there ---
so it comes down to the likelihood of spotting a match in some cases,
versus the wasted cycles of checking for a match in every query that
doesn't fit the pattern.
regards, tom lane
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