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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, 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 2024-09-06 12:05:40 +09:00
parent 565caaa79a
commit 3a97460970
1 changed files with 22 additions and 8 deletions
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30
src/backend/executor/execExpr.c
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@ -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 +4558,27 @@ 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.
*
* 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.
*/
jsestate->jump_error = state->steps_len;
if (jsexpr->on_error &&
jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR &&
(!(IsA(jsexpr->on_error->expr, Const) &&
((Const *) jsexpr->on_error->expr)->constisnull) ||
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 +4628,19 @@ 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.
*/
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 &&
(!(IsA(jsexpr->on_empty->expr, Const) &&
((Const *) jsexpr->on_empty->expr)->constisnull) ||
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;