Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com> writes:
> I wonder why SortState is a ScanState. As far as I know ScanState
> means the node may need projection and/or qualification, or it scans
> some relation, but Sort actually doesn't do such things.
No, not really. Per the comment for ScanState:
* ScanState extends PlanState for node types that represent
* scans of an underlying relation. It can also be used for nodes
* that scan the output of an underlying plan node --- in that case,
* only ScanTupleSlot is actually useful, and it refers to the tuple
* retrieved from the subplan.
It might be that we don't actually need ScanTupleSlot right now in the
implementation of Sort, but I don't see a good reason to remove the
field. We might just have to put it back later.
BTW, Sort is not the only node type like this --- I see at least
Material that's not projection-capable but has a ScanState.
regards, tom lane
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