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 <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

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;