v2-0004-SQL-JSON-Avoid-initializing-unnecessary-ON-ERROR-.patch

From bfded37e0439ab9397197c165b7bbf1618fe29dd Mon Sep 17 00:00:00 2001
From: Amit Langote <amitlan@postgresql.org>
Date: Mon, 2 Sep 2024 16:48:58 +0900
Subject: [PATCH v2 4/4] SQL/JSON: Avoid initializing unnecessary ON ERROR / ON
 EMPTY steps

When the ON ERROR / ON EMPTY behavior is to return NULL (the default
for JSON_VALUE() and JSON_QUERY()), returning NULL directly from
ExecEvalJsonExprPath() suffices. Therefore, there's no need to create
separate steps to check the error/empty flag or those to evaluate the
the constant NULL expression. However, these steps are necessary if
the RETURNING type is a domain, as constraints on the domain may need
to be checked.

Reported-by: Jian He <jian.universality@gmail.com>
Author: Jian He <jian.universality@gmail.com>
Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
---
 src/backend/executor/execExpr.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index 63289ee35e..eb1621ae75 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -4414,6 +4414,8 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 	ErrorSaveContext *escontext =
 		jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR ?
 		&jsestate->escontext : NULL;
+	bool		returning_domain =
+		get_typtype(jsexpr->returning->typid) == TYPTYPE_DOMAIN;
 
 	jsestate->jsexpr = jsexpr;
 
@@ -4556,20 +4558,21 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 		ExprEvalPushStep(state, scratch);
 	}
 
-	jsestate->jump_empty = jsestate->jump_error = -1;
-
 	/*
 	 * Step to check jsestate->error and return the ON ERROR expression if
 	 * there is one.  This handles both the errors that occur during jsonpath
 	 * evaluation in EEOP_JSONEXPR_PATH and subsequent coercion evaluation.
+	 *
+	 * Only add the extra steps for a NULL-valued expression when RETURNING a
+	 * domain type to check the constraints, if any.
 	 */
+	jsestate->jump_error = state->steps_len;
 	if (jsexpr->on_error &&
-		jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
+		jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR &&
+		(jsexpr->on_error->btype != JSON_BEHAVIOR_NULL || returning_domain))
 	{
 		ErrorSaveContext *saved_escontext;
 
-		jsestate->jump_error = state->steps_len;
-
 		/* JUMP to end if false, that is, skip the ON ERROR expression. */
 		jumps_to_end = lappend_int(jumps_to_end, state->steps_len);
 		scratch->opcode = EEOP_JUMP_IF_NOT_TRUE;
@@ -4619,14 +4622,17 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 	/*
 	 * Step to check jsestate->empty and return the ON EMPTY expression if
 	 * there is one.
+	 *
+	 * Only add the extra steps for a NULL-valued expression when RETURNING a
+	 * domain type to check the constraints, if any.
 	 */
+	jsestate->jump_empty = state->steps_len;
 	if (jsexpr->on_empty != NULL &&
-		jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR)
+		jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR &&
+		(jsexpr->on_empty->btype != JSON_BEHAVIOR_NULL || returning_domain))
 	{
 		ErrorSaveContext *saved_escontext;
 
-		jsestate->jump_empty = state->steps_len;
-
 		/* JUMP to end if false, that is, skip the ON EMPTY expression. */
 		jumps_to_end = lappend_int(jumps_to_end, state->steps_len);
 		scratch->opcode = EEOP_JUMP_IF_NOT_TRUE;
-- 
2.43.0