回复：[Internet]Re: [PATCH] Prevent replacement of a function if it's used in an index expression and is not IMMUTABLE

Hi hackers,

Thanks for the valuable feedback on my previous patch.

Based on the review comments, I have updated the patch as follows:

- Limited the error trigger only to the case where the original function is IMMUTABLE but the new definition is not.
- Changed the error code to ERRCODE_FEATURE_NOT_SUPPORTED for better semantics.
- Improved code indentation and style to align with project conventions.
- Added a regression test case in create_function_sql.sql to verify the new behavior.

The full updated patch is attached below.

Please take a look at this revised version. I look forward to your feedback and suggestions.

Best regards,  
xiaojiluo (Tencent Yunding Lab)

jian he<jian(dot)universality(at)gmail(dot)com&gt;&nbsp;在 2025年7月9日 周三 10:34 写道：

On Mon, Jun 30, 2025 at 5:34 PM sundayjiang(蒋浩天)
<sundayjiang(at)tencent(dot)com&gt; wrote:
&gt;
&gt; The purpose of this patch is to prevent replacing a function via `CREATE OR REPLACE FUNCTION` with a new definition that is not marked as `IMMUTABLE`, if the existing function is referenced by an index expression.
&gt;
&gt; Replacing such functions may lead to index corruption or runtime semantic inconsistencies, especially when the function’s output is not stable for the same input.
&gt;
&gt; If a function is used in an index, it can only be replaced if it is declared as `IMMUTABLE`.
&gt;

looking at the right above code ``if (oldproc-&gt;prokind != prokind)``

+ if(oldproc-&gt;prokind == PROKIND_FUNCTION &amp;&amp; volatility !=
PROVOLATILE_IMMUTABLE){

we can change it to

+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if(prokind == PROKIND_FUNCTION &amp;&amp; oldproc-&gt;provolatile ==
PROVOLATILE_IMMUTABLE &amp;&amp;
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; volatility != PROVOLATILE_IMMUTABLE)
&nbsp;+&nbsp;&nbsp;&nbsp;&nbsp; {
curly brace generally begins with a new line.

if (index_found)
+ ereport(ERROR,
+ (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
+ errmsg("cannot replace function \"%s\" with a non-IMMUTABLE function
because it is used by an index",
+ procedureName)));
Here, errcode ERRCODE_FEATURE_NOT_SUPPORTED would be more appropriate.

you can add a simple test in src/test/regress/sql/create_function_sql.sql
for example:
CREATE OR REPLACE FUNCTION get_a_int(int default 2) RETURNS int
IMMUTABLE AS 'select $1' LANGUAGE sql;
create table t1(a int);
create index on t1((get_a_int(a)));
CREATE OR REPLACE FUNCTION get_a_int(int default 2) RETURNS int AS
'select $1' LANGUAGE sql;