We usually say about 200 unique values as a limit for
gist_int_ops.
On Wed, 18 Mar 2009, Tom Lane wrote:
Ron Mayer <rm_pg@xxxxxxxxxxxxxxxxxxxxxxx> writes:
Oleg Bartunov wrote:
OB:> it's not about short or long arrays, it's about small or big
OB:> cardinality of the whole set (the number of unique elements)
I'm re-reading the docs and still wasn't obvious to me. A
potential docs patch is attached below.
Done, though not in exactly those words. I wonder though if we can
be less vague about it --- can we suggest a typical cutover point?
Like "use gist__intbig_ops if there are more than about 10,000 distinct
array values"? Even a rough order of magnitude for where to worry
about this would save a lot of people time.
regards, tom lane
Index: intarray.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/intarray.sgml,v
retrieving revision 1.5
retrieving revision 1.6
diff -c -r1.5 -r1.6
*** intarray.sgml 10 Dec 2007 05:32:51 -0000 1.5
--- intarray.sgml 18 Mar 2009 20:18:18 -0000 1.6
***************
*** 237,245 ****
<para>
Two GiST index operator classes are provided:
<literal>gist__int_ops</> (used by default) is suitable for
! small and medium-size arrays, while
<literal>gist__intbig_ops</> uses a larger signature and is more
! suitable for indexing large arrays.
</para>
<para>
--- 237,246 ----
<para>
Two GiST index operator classes are provided:
<literal>gist__int_ops</> (used by default) is suitable for
! small- to medium-size data sets, while
<literal>gist__intbig_ops</> uses a larger signature and is more
! suitable for indexing large data sets (i.e., columns containing
! a large number of distinct array values).
</para>
<para>
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@xxxxxxxxxx, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83
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