fix: avoid full scan for metadata-only projections with _pos - #2995
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anoopj wants to merge 1 commit into
Open
fix: avoid full scan for metadata-only projections with _pos#2995anoopj wants to merge 1 commit into
anoopj wants to merge 1 commit into
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A projection of only metadata columns leaves the data field-id list empty, which get_arrow_projection_mask maps to reading all columns (so a bare COUNT(*) still gets a row count). When _pos is projected, the RowNumber virtual column supplies the row count independently of the data columns, so read no data columns instead of all of them. Pure-constant and empty projections keep the read-all behavior, since they have no other row source.
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Which issue does this PR close?
What changes are included in this PR?
A projection of only metadata columns leaves the data field-id list empty, which get_arrow_projection_mask maps to reading all columns (so a bare COUNT(*) still gets a row count). When _pos is projected, the RowNumber virtual column supplies the row count independently of the data columns, so read no data columns instead of all of them. Pure-constant and empty projections keep the read-all behavior, since they have no other row source.
Are these changes tested?
Added several tests