diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 57 |
1 files changed, 0 insertions, 57 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index ac945ca4d19..d8e1282e128 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -6304,63 +6304,6 @@ SELECT * FROM parent WHERE key = 2400; </listitem> </varlistentry> - <varlistentry id="guc-or-to-any-transform-limit" xreflabel="or_to_any_transform_limit"> - <term><varname>or_to_any_transform_limit</varname> (<type>boolean</type>) - <indexterm> - <primary><varname>or_to_any_transform_limit</varname> configuration parameter</primary> - </indexterm> - </term> - <listitem> - <para> - Sets the minimum length of arguments in an <literal>OR</literal> - expression exceeding which planner will try to lookup and group - multiple similar <literal>OR</literal> expressions to - <literal>ANY</literal> (<xref linkend="functions-comparisons-any-some"/>) - expressions. The grouping technique of this transformation is based - on the equivalence of variable sides. One side of such an expression - must be a constant clause, and the other must contain a variable - clause. The default value is <literal>5</literal>. The value of - <literal>-1</literal> completely disables the transformation. - </para> - <para> - The advantage of this <literal>OR-to-ANY</literal> transformation is - faster query planning and execution. In certain cases, this - transformation also leads to more effective plans containing - a single index scan instead of multiple bitmap scans. However, it - may also cause a planning regression when distinct - <literal>OR</literal> arguments are better to match to distinct indexes. - This may happen when they have different matching partial indexes or - have different distributions of other columns used in the query. - Generally, more groupable <literal>OR</literal> arguments mean that - transformation will be more likely to win than to lose. - </para> - <para> - For example, this query has its set of five <literal>OR</literal> - expressions transformed to <literal>ANY</literal> with the default - value of <varname>or_to_any_transform_limit</varname>. But not with - the increased value. -<programlisting> -# EXPLAIN SELECT * FROM tbl WHERE key = 1 OR key = 2 OR key = 3 OR key = 4 OR key = 5; - QUERY PLAN ------------------------------------------------------ - Seq Scan on tbl (cost=0.00..51.44 rows=64 width=4) - Filter: (key = ANY ('{1,2,3,4,5}'::integer[])) -(2 rows) - -# SET or_to_any_transform_limit = 6; -SET - -# EXPLAIN SELECT * FROM tbl WHERE key = 1 OR key = 2 OR key = 3 OR key = 4 OR key = 5; - QUERY PLAN ---------------------------------------------------------------------------- - Seq Scan on tbl (cost=0.00..67.38 rows=63 width=4) - Filter: ((key = 1) OR (key = 2) OR (key = 3) OR (key = 4) OR (key = 5)) -(2 rows) -</programlisting> - </para> - </listitem> - </varlistentry> - <varlistentry id="guc-plan-cache-mode" xreflabel="plan_cache_mode"> <term><varname>plan_cache_mode</varname> (<type>enum</type>) <indexterm> |