Re: BUG #18830: ExecInitMerge Segfault on MERGE

Amit Langote <amitlangote09(at)gmail(dot)com> 于2025年3月4日周二 19:51写道：

> On Mon, Mar 3, 2025 at 9:16 PM Tender Wang <tndrwang(at)gmail(dot)com> wrote:
> > nrels = list_length(resultRelations);
> > ...
> > mtstate->resultRelInfo = (ResultRelInfo *)
> > palloc(nrels * sizeof(ResultRelInfo));
> >
> > The memory of mtstate->resultRelInfo point to is undefined. When we
> access its memory in ExecInitMerge(),
>
> This needs to be fixed saparately.
>
> > relationDesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
> >
> > crash happened.
>
> Do you have a case where this access to undefined
> ModifyTableState.resultRelInfo occurs? I would have thought that it
> should not happen.
>

"undefined" may not be accurate, "invalid" seems more correct.
I still use the case:
merge into part_abc_view pt
using (select stable_one() + 2 as pid) as q join part_abc_1 pt1 on (true)
on pt.a = stable_one() +2
when not matched then insert values(1, 'd', false);

(gdb) p *resultRelInfo
$5 = {type = 2139062142, ri_RangeTableIndex = 2139062143, ri_RelationDesc =
0x180, ri_NumIndices = 195, ri_IndexRelationDescs = 0x500000182,
ri_IndexRelationInfo = 0x7f8773b2aa38, ri_RowIdAttNo = 0,
ri_extraUpdatedCols = 0x0, ri_projectNew = 0x0,
ri_newTupleSlot = 0x0, ri_oldTupleSlot = 0x0, ri_projectNewInfoValid =
false, ri_needLockTagTuple = false, ri_TrigDesc = 0x0, ri_TrigFunctions =
0x0, ri_TrigWhenExprs = 0x0, ri_TrigInstrument = 0x0, ri_ReturningSlot =
0x0, ri_TrigOldSlot = 0x0,
ri_TrigNewSlot = 0x0, ri_AllNullSlot = 0x0, ri_FdwRoutine = 0x0,
ri_FdwState = 0x0, ri_usesFdwDirectModify = false, ri_NumSlots = 0,
ri_NumSlotsInitialized = 0, ri_BatchSize = 0, ri_Slots = 0x0, ri_PlanSlots
= 0x0, ri_WithCheckOptions = 0x0,
ri_WithCheckOptionExprs = 0x0, ri_ConstraintExprs = 0x0,
ri_GeneratedExprsI = 0x0, ri_GeneratedExprsU = 0x0, ri_NumGeneratedNeededI
= 0, ri_NumGeneratedNeededU = 0, ri_returningList = 0x0,
ri_projectReturning = 0x0,
ri_onConflictArbiterIndexes = 0x0, ri_onConflict = 0x0, ri_MergeActions =
{0x0, 0x0, 0x0}, ri_MergeJoinCondition = 0x0, ri_PartitionCheckExpr = 0x0,
ri_ChildToRootMap = 0x0, ri_ChildToRootMapValid = false, ri_RootToChildMap
= 0x0,
ri_RootToChildMapValid = false, ri_RootResultRelInfo = 0x0,
ri_PartitionTupleSlot = 0x0, ri_CopyMultiInsertBuffer = 0x0,
ri_ancestorResultRels = 0x0}

ri_RelationDesc = 0x180, this address is not invalid.

--
Thanks,
Tender Wang