Re: What is wrong with hashed index usage?

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > I remember three problems: build time, index size, and concurrency
> > problems. I was wondering about the equal key case myself, and assumed
> > hash may be a win there, but with the concurrency problems, is that even
> > possible?
>
> Sure. Many-equal-keys are a problem for btree whether you have any
> concurrency or not.
>
> > OK, I have reworded it. Is that better?
>
> It's better, but you've still discarded the original's explicit mention
> of concurrency problems. Why do you want to remove information?

OK, concurrency added. How is that?

>
> > How about an elog(NOTICE) for hash use?
>
> I don't think that's appropriate.

I was thinking of this during CREATE INDEX ... hash:

NOTICE: Hash index use is discouraged. See the CREATE INDEX
reference page for more information.

Does anyone else like/dislike that?

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