diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/executor/nodeSubplan.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c index 43b36dcd3b4..434c72c9f20 100644 --- a/src/backend/executor/nodeSubplan.c +++ b/src/backend/executor/nodeSubplan.c @@ -245,6 +245,21 @@ ExecScanSubPlan(SubPlanState *node, * ones, so this should be safe.) Unlike ExecReScanSetParamPlan, we do * *not* set bits in the parent plan node's chgParam, because we don't * want to cause a rescan of the parent. + * + * Note: we are also relying on MULTIEXPR SubPlans not sharing any output + * parameters with other SubPlans, because if one does then it is unclear + * which SubPlanState node the parameter's execPlan field will be pointing + * to when we come to evaluate the parameter. We can allow plain initplan + * SubPlans to share output parameters, because it doesn't actually matter + * which initplan SubPlan we reference as long as they all point to the + * same underlying subplan. However, that fails to hold for MULTIEXPRs + * because they can have non-empty args lists, and the "same" args might + * have mutated into different forms in different parts of a plan tree. + * There is currently no problem because MULTIEXPR can appear only in an + * UPDATE's top-level target list, so it won't get duplicated anyplace. + * Postgres versions before v14 had to make concrete efforts to avoid + * sharing output parameters across different clones of a MULTIEXPR, and + * the problem could recur someday. */ if (subLinkType == MULTIEXPR_SUBLINK) { |