Tom Lane wrote:
> Bruce Momjian <[EMAIL PROTECTED]> 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?
--
Bruce Momjian | http://candle.pha.pa.us
[EMAIL PROTECTED] | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
Index: doc/src/sgml/indices.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v
retrieving revision 1.32
diff -c -r1.32 indices.sgml
*** doc/src/sgml/indices.sgml 21 Jun 2002 03:25:53 -0000 1.32
--- doc/src/sgml/indices.sgml 21 Jun 2002 15:00:32 -0000
***************
*** 181,188 ****
</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.
</para>
</note>
--- 181,188 ----
</synopsis>
<note>
<para>
! Testing has shown hash indexes to be similar or slower than btree indexes,
! and the index size and build time for hash indexes is much worse. For
these reasons, hash index use is discouraged.
</para>
</note>
Index: doc/src/sgml/ref/create_index.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v
retrieving revision 1.32
diff -c -r1.32 create_index.sgml
*** doc/src/sgml/ref/create_index.sgml 21 Jun 2002 03:25:53 -0000 1.32
--- doc/src/sgml/ref/create_index.sgml 21 Jun 2002 15:00:32 -0000
***************
*** 330,337 ****
the <literal>=</literal> operator.
</para>
<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.
</para>
--- 330,337 ----
the <literal>=</literal> operator.
</para>
<para>
! Testing has shown hash indexes to be similar or slower than btree indexes,
! and the index size and build time for hash indexes is much worse. For
these reasons, hash index use is discouraged.
</para>
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