v8-0002-add-function-DomainHaveVolatileConstraints.patch

From e797885a884cfda7e13eb237c277ad216710cc94 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Mon, 26 Jan 2026 15:05:56 +0800
Subject: [PATCH v8 2/3] add function DomainHaveVolatileConstraints

Returns true if the Domain has any constraints.  If you want check this domain
have any volatile check constraints, make sure argument have_volatile is not
NULL.
We can avoid a table rewrite when adding or modifying a column with a
constrained domain, but only if the domain's constraints are not volatile.
Therefore function DomainHaveVolatileConstraints is necessary to check
constraint volatility.

discussion: https://postgr.es/m/CACJufxE_+iZBR1i49k_AHigppPwLTJi6km8NOsC7FWvKdEmmXg@mail.gmail.com
commitfest: https://commitfest.postgresql.org/patch/5641
---
 src/backend/utils/cache/typcache.c | 37 ++++++++++++++++++++++++++++++
 src/include/utils/typcache.h       |  1 +
 2 files changed, 38 insertions(+)

diff --git a/src/backend/utils/cache/typcache.c b/src/backend/utils/cache/typcache.c
index dc4b1a56414..d00cfd471ae 100644
--- a/src/backend/utils/cache/typcache.c
+++ b/src/backend/utils/cache/typcache.c
@@ -1499,6 +1499,43 @@ DomainHasConstraints(Oid type_id)
 }
 
 
+/*
+ * Check whether a domain has any constraints, and determine if any of those
+ * constraints contain volatile expressions.
+ *
+ * To detect volatile expressions within domain check constraints, ensure that
+ * have_volatile is not NULL. If have_volatile is NULL, this function behave the
+ * same as DomainHasConstraints.
+ */
+bool
+DomainHaveVolatileConstraints(Oid type_id, bool *have_volatile)
+{
+	/*
+	 * Note: a side effect is to cause the typcache's domain data to become
+	 * valid.  This is fine since we'll likely need it soon if there is any.
+	 */
+	TypeCacheEntry *typentry = lookup_type_cache(type_id, TYPECACHE_DOMAIN_CONSTR_INFO);
+
+	if (typentry->domainData != NULL)
+	{
+		foreach_node(DomainConstraintState, constrstate, typentry->domainData->constraints)
+		{
+			if (constrstate->constrainttype == DOM_CONSTRAINT_CHECK &&
+				contain_volatile_functions((Node *) constrstate->check_expr))
+			{
+				if (have_volatile)
+					*have_volatile = true;
+
+				break;
+			}
+		}
+
+		return true;
+	}
+
+	return false;
+}
+
 /*
  * array_element_has_equality and friends are helper routines to check
  * whether we should believe that array_eq and related functions will work
diff --git a/src/include/utils/typcache.h b/src/include/utils/typcache.h
index 0e3945aa244..d9e894b1146 100644
--- a/src/include/utils/typcache.h
+++ b/src/include/utils/typcache.h
@@ -184,6 +184,7 @@ extern void InitDomainConstraintRef(Oid type_id, DomainConstraintRef *ref,
 extern void UpdateDomainConstraintRef(DomainConstraintRef *ref);
 
 extern bool DomainHasConstraints(Oid type_id);
+extern bool DomainHaveVolatileConstraints(Oid type_id, bool *have_volatile);
 
 extern TupleDesc lookup_rowtype_tupdesc(Oid type_id, int32 typmod);
 
-- 
2.34.1