Re: What is wrong with hashed index usage?

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > <para>
> > ! Because of the limited utility of hash indexes, a B-tree index
> > ! should generally be preferred over a hash index. We do not have
> > ! sufficient evidence that hash indexes are actually faster than
> > ! B-trees even for <literal>=</literal> comparisons. Moreover,
> > ! hash indexes require coarser locks; see <xref
> > ! linkend="locking-indexes">.
> > </para>
> > </note>
> > </para>
> > --- 181,189 ----
> > </synopsis>
> > <note>
> > <para>
> > ! Testing has shown that hash indexes are slower than btree indexes,
> > ! and the size and build time for hash indexes is much worse. For
> > ! these reasons, hash index use is discouraged.
>
> This change strikes me as a step backwards. The existing wording tells
> the truth; the proposed revision removes the facts in favor of a blanket
> assertion that is demonstrably false.

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.

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