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Commit3a97460

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SQL/JSON: Avoid initializing unnecessary ON ERROR / ON EMPTY steps
When the ON ERROR / ON EMPTY behavior is to return NULL, returningNULL directly from ExecEvalJsonExprPath() suffices. Therefore, there'sno need to create separate steps to check the error/empty flag orthose to evaluate the the constant NULL expression. This speeds upcommon cases because the default ON ERROR / ON EMPTY behavior forJSON_QUERY() and JSON_VALUE() is to return NULL. However, these stepsare necessary if the RETURNING type is a domain, as constraints on thedomain 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.comBackpatch-through: 17
1 parent565caaa commit3a97460

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‎src/backend/executor/execExpr.c

Lines changed: 22 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -4414,6 +4414,8 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
44144414
ErrorSaveContext*escontext=
44154415
jsexpr->on_error->btype!=JSON_BEHAVIOR_ERROR ?
44164416
&jsestate->escontext :NULL;
4417+
boolreturning_domain=
4418+
get_typtype(jsexpr->returning->typid)==TYPTYPE_DOMAIN;
44174419

44184420
jsestate->jsexpr=jsexpr;
44194421

@@ -4556,20 +4558,27 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
45564558
ExprEvalPushStep(state,scratch);
45574559
}
45584560

4559-
jsestate->jump_empty=jsestate->jump_error=-1;
4560-
45614561
/*
45624562
* Step to check jsestate->error and return the ON ERROR expression if
45634563
* there is one. This handles both the errors that occur during jsonpath
45644564
* evaluation in EEOP_JSONEXPR_PATH and subsequent coercion evaluation.
4565+
*
4566+
* Speed up common cases by avoiding extra steps for a NULL-valued ON
4567+
* ERROR expression unless RETURNING a domain type, where constraints must
4568+
* be checked. ExecEvalJsonExprPath() already returns NULL on error,
4569+
* making additional steps unnecessary in typical scenarios. Note that the
4570+
* default ON ERROR behavior for JSON_VALUE() and JSON_QUERY() is to
4571+
* return NULL.
45654572
*/
4573+
jsestate->jump_error=state->steps_len;
45664574
if (jsexpr->on_error&&
4567-
jsexpr->on_error->btype!=JSON_BEHAVIOR_ERROR)
4575+
jsexpr->on_error->btype!=JSON_BEHAVIOR_ERROR&&
4576+
(!(IsA(jsexpr->on_error->expr,Const)&&
4577+
((Const*)jsexpr->on_error->expr)->constisnull)||
4578+
returning_domain))
45684579
{
45694580
ErrorSaveContext*saved_escontext;
45704581

4571-
jsestate->jump_error=state->steps_len;
4572-
45734582
/* JUMP to end if false, that is, skip the ON ERROR expression. */
45744583
jumps_to_end=lappend_int(jumps_to_end,state->steps_len);
45754584
scratch->opcode=EEOP_JUMP_IF_NOT_TRUE;
@@ -4619,14 +4628,19 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
46194628
/*
46204629
* Step to check jsestate->empty and return the ON EMPTY expression if
46214630
* there is one.
4631+
*
4632+
* See the comment above for details on the optimization for NULL-valued
4633+
* expressions.
46224634
*/
4635+
jsestate->jump_empty=state->steps_len;
46234636
if (jsexpr->on_empty!=NULL&&
4624-
jsexpr->on_empty->btype!=JSON_BEHAVIOR_ERROR)
4637+
jsexpr->on_empty->btype!=JSON_BEHAVIOR_ERROR&&
4638+
(!(IsA(jsexpr->on_empty->expr,Const)&&
4639+
((Const*)jsexpr->on_empty->expr)->constisnull)||
4640+
returning_domain))
46254641
{
46264642
ErrorSaveContext*saved_escontext;
46274643

4628-
jsestate->jump_empty=state->steps_len;
4629-
46304644
/* JUMP to end if false, that is, skip the ON EMPTY expression. */
46314645
jumps_to_end=lappend_int(jumps_to_end,state->steps_len);
46324646
scratch->opcode=EEOP_JUMP_IF_NOT_TRUE;

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