Re: What is wrong with hashed index usage?

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > OK, which part of is "demonstrably false"? I think the old "should
> > generally be preferred" is too vague. No one has come up with a case
> > where hash has shown to be faster, and a lot of cases where it is slower.
>
> The only thing I recall being lots worse is initial index build.
>
> I have not tested it much, but I would expect that hash holds up better
> in the presence of many equal keys than btree does...

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?

OK, I have reworded it. Is that better? How about an elog(NOTICE) for
hash use?

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