[jira] [Created] (KUDU-3784) Support scan predicates on columns that are not in the projection

["Gabriella Lotz (Jira)" <ji...@apache.org>]

Gabriella Lotz created KUDU-3784:
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             Summary: Support scan predicates on columns that are not in the projection
                 Key: KUDU-3784
                 URL: https://issues.apache.org/jira/browse/KUDU-3784
             Project: Kudu
          Issue Type: Improvement
            Reporter: Gabriella Lotz


When a scan projects no (or few) columns but has predicates on columns outside the projection, those predicates cannot be evaluated by the MaterializingIterator. The most common case is a counting scan (SELECT count(...)) with predicates that are not folded into the key range.

Today these out-of-projection predicates are skipped (see the TODO in MaterializingIterator::Init). This is safe on the server scan path because TabletServiceImpl adds predicate columns to the projection via ScanSpec::GetMissingColumns(), so the only skipped predicates are redundant ones lifted from the rowset's primary key bounds. But the lower-level scan path (no missing-column expansion) has no such guarantee, so a genuine predicate could be silently dropped.

Proper fix: materialize the needed columns (or otherwise evaluate the predicate) instead of skipping, so predicates on non-projected columns are honored generally. The disabled case TestPushdownIntValueRange (count-only path) in tablet-pushdown-test.cc should be re-enabled as part of this.



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