opt: add SerializingProject exec primitive #52386
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Reviewed 7 of 7 files at r1.
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The top-level projection of a query has a special property - it can project away columns that we want an ordering on (e.g. `SELECT a FROM t ORDER BY b`). The distsql physical planner was designed to tolerate such cases, as they were much more common with the heuristic planner. But the new distsql exec factory does not; it currently relies on a hack: it detects this case by checking if the required output ordering is `nil`. This is fragile and doesn't work in all cases. This change adds a `SerializingProject` primitive which is like a SimpleProject but it forces serialization of all parallel streams into one. The new primitive is used to enforce the final query presentation. We only need to pass column names for the presentation, so we remove `RenameColumns` and remove the column names argument from `SimpleProject` (simplifying some execbuilder code). We also fix a bug in `ConstructSimpleProject` where we weren't taking the `PlanToStreamColMap` into account when building the projection. Release note: None
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The top-level projection of a query has a special property - it can project away
columns that we want an ordering on (e.g.
SELECT a FROM t ORDER BY b).The distsql physical planner was designed to tolerate such cases, as they were
much more common with the heuristic planner. But the new distsql exec factory
does not; it currently relies on a hack: it detects this case by checking if the
required output ordering is
nil. This is fragile and doesn't work in allcases.
This change adds a
SerializingProjectprimitive which is like a SimpleProjectbut it forces serialization of all parallel streams into one. The new primitive
is used to enforce the final query presentation. We only need to pass column
names for the presentation, so we remove
RenameColumnsand remove the columnnames argument from
SimpleProject(simplifying some execbuilder code).We also fix a bug in
ConstructSimpleProjectwhere we weren't taking thePlanToStreamColMapinto account when building the projection.Release note: None