Sort is actually PlanState?
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. I also tried
to modify SortState as PlanState as in the attached patch and
regression test passed. Do I misunderstand ScanState?
Regards,
--
Hitoshi Harada
Attachments:
sort-plan.20101102.patchapplication/octet-stream; name=sort-plan.20101102.patchDownload+16-21
Hitoshi Harada <umi.tanuki@gmail.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
2010/11/2 Tom Lane <tgl@sss.pgh.pa.us>:
Hitoshi Harada <umi.tanuki@gmail.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.
Regards,
--
Hitoshi Harada