On Wed, Dec 21, 2022 at 6:44 AM Michael Paquier <mich...@paquier.xyz> wrote:
>
> I have applied v2-0001.
Thanks for taking care of this.
By seeing the impact that get_call_result_type() can have for the
functions that are possibly called repeatedly, I couldn't resist
sharing a patch (attached herewith) that adds a note of caution and
another way to build TupleDesc in the documentation to help developers
out there. Thoughts?
--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
From 3ee0c4a402bcf2d25a7c544ddd60d3e9742b9048 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Wed, 21 Dec 2022 06:38:27 +0000
Subject: [PATCH v1] Add another way to build TupleDesc in documentation
---
doc/src/sgml/xfunc.sgml | 44 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index cf5810b3c1..8b9c718fdf 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -2839,6 +2839,35 @@ TypeFuncClass get_call_result_type(FunctionCallInfo fcinfo,
cannot accept type record</quote>.)
</para>
+ <para>
+ Another way to setup <structname>TupleDesc</structname> is to use the
+ following functions:
+<programlisting>
+TupleDesc CreateTemplateTupleDesc(int natts);
+void TupleDescInitEntry(TupleDesc desc,
+ AttrNumber attributeNumber,
+ const char *attributeName,
+ Oid oidtypeid,
+ int32 typmod,
+ int attdim);
+TupleDesc BlessTupleDesc(TupleDesc tupdesc);
+</programlisting>
+ For example:
+<programlisting>
+ /*
+ * Construct a tuple descriptor for the result row. The number of output
+ * columns, column names and types must match the function's pg_proc entry
+ * or function's definition.
+ */
+ tupdesc = CreateTemplateTupleDesc(4);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 1, "foo", INT4OID, -1, 0);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 2, "bar", BOOLOID, -1, 0);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 3, "baz", TEXTOID, -1, 0);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 4, "qux", TIMESTAMPTZOID, -1, 0);
+ tupdesc = BlessTupleDesc(tupdesc);
+</programlisting>
+ </para>
+
<tip>
<para>
<function>get_call_result_type</function> can resolve the actual type of a
@@ -2849,6 +2878,21 @@ TypeFuncClass get_call_result_type(FunctionCallInfo fcinfo,
</para>
</tip>
+ <note>
+ <para>
+ <function>get_call_result_type</function> is relatively expensive
+ as it has to look up system catalogs and do other things to setup
+ <structname>TupleDesc</structname>. While it is recommended
+ in most of the cases, remember to consider setting up
+ <structname>TupleDesc</structname> with
+ <function>CreateTemplateTupleDesc</function>,
+ <function>TupleDescInitEntry</function> and
+ <function>BlessTupleDesc</function> as shown above, if the function
+ returns set or the function is possible used repeatedly
+ (monitoring purposes, for instance).
+ </para>
+ </note>
+
<note>
<para>
<function>get_call_result_type</function> has a sibling
--
2.34.1
