2010/11/2 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> 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.
It might reduce a few cycle used in initializing and cleaning of
ScanTupleSlot, but I basically agree it's not good reason to do it.
> BTW, Sort is not the only node type like this --- I see at least
> Material that's not projection-capable but has a ScanState.
Yes, during designing DtScan which is coming in the writeable CTEs I
came up with the question.
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