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Fix ndistinct estimates with system attributes
When estimating the number of groups using extended statistics, the code was discarding information about system attributes. This led to strange situation that SELECT 1 FROM t GROUP BY ctid; could have produced higher estimate (equal to pg_class.reltuples) than SELECT 1 FROM t GROUP BY a, b, ctid; with extended statistics on (a,b). Fixed by retaining information about the system attribute. Backpatch all the way to 10, where extended statistics were introduced. Author: Tomas Vondra Backpatch-through: 10
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@ -3851,11 +3851,11 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
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attnum = ((Var *) varinfo->var)->varattno;
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if (!AttrNumberIsForUserDefinedAttr(attnum))
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if (AttrNumberIsForUserDefinedAttr(attnum) &&
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bms_is_member(attnum, matched))
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continue;
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if (!bms_is_member(attnum, matched))
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newlist = lappend(newlist, varinfo);
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newlist = lappend(newlist, varinfo);
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}
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*varinfos = newlist;
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