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Commit82849df

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Add new selectivity estimation functions for pattern-matching operators
(LIKE and regexp matches). These are not yet referenced in pg_operator,so by default the system will continue to use eqsel/neqsel.Also, tweak convert_to_scalar() logic so that common prefixes of stringsare stripped off, allowing better accuracy when all strings in a tableshare a common prefix.
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‎doc/src/sgml/xoper.sgml

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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.9 2000/03/31 03:27:41 thomas Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.10 2000/04/16 04:41:01 tgl Exp $
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-->
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<Chapter Id="xoper">
@@ -254,9 +254,9 @@ SELECT (a + b) AS c FROM test_complex;
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<para>
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You can frequently get away with using either eqsel or neqsel for
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operators that have very high or very low selectivity, even if they
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aren't really equality or inequality. For example, the regular expression
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matchingoperators(~, ~*, etc)use eqsel on the assumption that they'll
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usually only match a small fraction of the entries in a table.
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aren't really equality or inequality. For example, the
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approximate-equality geometricoperators use eqsel on the assumption that
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they'llusually only match a small fraction of the entries in a table.
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</para>
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<para>

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