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SQL/JSON: Avoid initializing unnecessary ON ERROR / ON EMPTY steps

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When the ON ERROR / ON EMPTY behavior is to return NULL, 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.  This speeds up
common cases because the default ON ERROR / ON EMPTY behavior for
JSON_QUERY() and JSON_VALUE() is to return NULL.  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
Backpatch-through: 17
This commit is contained in:
Amit Langote 2024-09-09 13:46:58 +09:00
parent 87b6c3c0b7
commit dd8bea88ab
2 changed files with 34 additions and 12 deletions
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32
src/backend/executor/execExpr.c
View File

@ -4411,9 +4411,11 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
List *jumps_return_null = NIL;
List *jumps_to_end = NIL;
ListCell *lc;
ErrorSaveContext *escontext =
jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR ?
&jsestate->escontext : NULL;
ErrorSaveContext *escontext;
bool returning_domain =
get_typtype(jsexpr->returning->typid) == TYPTYPE_DOMAIN;
Assert(jsexpr->on_error != NULL);
jsestate->jsexpr = jsexpr;
@ -4491,6 +4493,9 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
scratch->d.constval.isnull = true;
ExprEvalPushStep(state, scratch);
escontext = jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR ?
&jsestate->escontext : NULL;
/*
* To handle coercion errors softly, use the following ErrorSaveContext to
* pass to ExecInitExprRec() when initializing the coercion expressions
@ -4562,9 +4567,18 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
* 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.
*
* Speed up common cases by avoiding extra steps for a NULL-valued ON
* ERROR expression unless RETURNING a domain type, where constraints must
* be checked. ExecEvalJsonExprPath() already returns NULL on error,
* making additional steps unnecessary in typical scenarios. Note that the
* default ON ERROR behavior for JSON_VALUE() and JSON_QUERY() is to
* return NULL.
*/
if (jsexpr->on_error &&
jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
if (jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR &&
(!(IsA(jsexpr->on_error->expr, Const) &&
((Const *) jsexpr->on_error->expr)->constisnull) ||
returning_domain))
{
ErrorSaveContext *saved_escontext;
@ -4619,9 +4633,15 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
/*
* Step to check jsestate->empty and return the ON EMPTY expression if
* there is one.
*
* See the comment above for details on the optimization for NULL-valued
* expressions.
*/
if (jsexpr->on_empty != NULL &&
jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR)
jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR &&
(!(IsA(jsexpr->on_empty->expr, Const) &&
((Const *) jsexpr->on_empty->expr)->constisnull) ||
returning_domain))
{
ErrorSaveContext *saved_escontext;

14
src/backend/executor/execExprInterp.c
View File

@ -4550,8 +4550,8 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
/* Set up to catch coercion errors of the ON EMPTY value. */
jsestate->escontext.error_occurred = false;
jsestate->escontext.details_wanted = true;
Assert(jsestate->jump_empty >= 0);
return jsestate->jump_empty;
/* Jump to end if the ON EMPTY behavior is to return NULL */
return jsestate->jump_empty >= 0 ? jsestate->jump_empty : jsestate->jump_end;
}
}
else if (jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
@ -4560,8 +4560,9 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
/* Set up to catch coercion errors of the ON ERROR value. */
jsestate->escontext.error_occurred = false;
jsestate->escontext.details_wanted = true;
Assert(!throw_error && jsestate->jump_error >= 0);
return jsestate->jump_error;
Assert(!throw_error);
/* Jump to end if the ON ERROR behavior is to return NULL */
return jsestate->jump_error >= 0 ? jsestate->jump_error : jsestate->jump_end;
}
if (jsexpr->column_name)
@ -4581,14 +4582,15 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
*/
if (error)
{
Assert(!throw_error && jsestate->jump_error >= 0);
Assert(!throw_error);
*op->resvalue = (Datum) 0;
*op->resnull = true;
jsestate->error.value = BoolGetDatum(true);
/* Set up to catch coercion errors of the ON ERROR value. */
jsestate->escontext.error_occurred = false;
jsestate->escontext.details_wanted = true;
return jsestate->jump_error;
/* Jump to end if the ON ERROR behavior is to return NULL */
return jsestate->jump_error >= 0 ? jsestate->jump_error : jsestate->jump_end;
}
return jump_eval_coercion >= 0 ? jump_eval_coercion : jsestate->jump_end;