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Add COST and ROWS options to CREATE/ALTER FUNCTION, plus underlying pg_proc

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columns procost and prorows, to allow simple user adjustment of the estimated
cost of a function call, as well as control of the estimated number of rows
returned by a set-returning function.  We might eventually wish to extend this
to allow function-specific estimation routines, but there seems to be
consensus that we should try a simple constant estimate first.  In particular
this provides a relatively simple way to control the order in which different
WHERE clauses are applied in a plan node, which is a Good Thing in view of the
fact that the recent EquivalenceClass planner rewrite made that much less
predictable than before.
This commit is contained in:
Tom Lane
2007-01-22 01:35:23 +00:00
parent a85e9c61e5
commit 5a7471c307
27 changed files with 2550 additions and 2090 deletions
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38
doc/src/sgml/ref/create_function.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.70 2006/11/10 20:52:18 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.71 2007/01/22 01:35:19 tgl Exp $
-->
<refentry id="SQL-CREATEFUNCTION">
@ -26,6 +26,8 @@ CREATE [ OR REPLACE ] FUNCTION
| IMMUTABLE | STABLE | VOLATILE
| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
| [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
| COST <replaceable class="parameter">execution_cost</replaceable>
| ROWS <replaceable class="parameter">result_rows</replaceable>
| AS '<replaceable class="parameter">definition</replaceable>'
| AS '<replaceable class="parameter">obj_file</replaceable>', '<replaceable class="parameter">link_symbol</replaceable>'
} ...
@ -52,7 +54,7 @@ CREATE [ OR REPLACE ] FUNCTION
</para>
<para>
To update the definition of an existing function, use
To replace the current definition of an existing function, use
<command>CREATE OR REPLACE FUNCTION</command>. It is not possible
to change the name or argument types of a function this way (if you
tried, you would actually be creating a new, distinct function).
@ -289,6 +291,35 @@ CREATE [ OR REPLACE ] FUNCTION
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">execution_cost</replaceable></term>
<listitem>
<para>
A positive number giving the estimated execution cost for the function,
in units of <xref linkend="guc-cpu-operator-cost">. If the function
returns a set, this is the cost per returned row. If the cost is
not specified, 1 unit is assumed for C-language and internal functions,
and 100 units for functions in all other languages. Larger values
cause the planner to try to avoid evaluating the function more often
than necessary.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">result_rows</replaceable></term>
<listitem>
<para>
A positive number giving the estimated number of rows that the planner
should expect the function to return. This is only allowed when the
function is declared to return a set. The default assumption is
1000 rows.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">definition</replaceable></term>
@ -400,7 +431,8 @@ CREATE FUNCTION foo(int, out text) ...
<para>
When repeated <command>CREATE FUNCTION</command> calls refer to
the same object file, the file is only loaded once. To unload and
the same object file, the file is only loaded once per session.
To unload and
reload the file (perhaps during development), use the <xref
linkend="sql-load" endterm="sql-load-title"> command.
</para>