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

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 <[email protected]>
Author: Jian He <[email protected]>
Author: Amit Langote <[email protected]>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index 63289ee35ee58ac36dc8fcce11b9251365b41f8f..c8077aa57bdd6c7f6e7eca2b7ed2c31c7b02c839 100644 (file)
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -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;
 

diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index a6c47f61e0d2ca2d8ea2e119c561305a7ff180f4..9fd988cc992f53d474a1b189b801c6c238203951 100644 (file)
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -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;