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https://issues.apache.org/jira/browse/CALCITE-7487?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alessandro Solimando updated CALCITE-7487:
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Component/s: core
> ProjectJoinTransposeRule throws ArrayIndexOutOfBoundsException in
> PushProjector when a Join input has a zero-column row type
> ----------------------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-7487
> URL: https://issues.apache.org/jira/browse/CALCITE-7487
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Chris Rice
> Priority: Minor
>
> h2. Description
> {{ProjectJoinTransposeRule}} (via {{PushProjector}}) throws
> {{ArrayIndexOutOfBoundsException}} when invoked on a {{Project}} over a
> {{Join}} whose left or right input has a row type with zero fields.
> The crash originates in a workaround introduced to avoid producing
> zero-column projections below the join. In {{PushProjector.locateAllRefs()}}
> (lines 456–471 at HEAD, {{95eecd87c}}):
> {code:java}
> if ((childRel instanceof Join)
> || (childRel instanceof SetOp)) {
> // if nothing is projected from the children, arbitrarily project
> // the first columns; this is necessary since Fennel doesn't
> // handle 0-column projections
> if (nProject == 0 && childPreserveExprs.isEmpty()) {
> projRefs.set(0);
> nProject = 1;
> }
> if (childRel instanceof Join) {
> if (nRightProject == 0 && rightPreserveExprs.isEmpty()) {
> projRefs.set(nFields);
> nRightProject = 1;
> }
> }
> }
> {code}
> The workaround forces {{nRightProject = 1}} and sets a bit at position
> {{nFields}} (the first field of the right input). When {{nFieldsRight == 0}}
> this bit points past the last valid field of the right input entirely.
> {{createProjectRefsAndExprs}} later reads that bit and uses it to index into
> the right input's field list, which is empty:
> {code:java}
> // PushProjector.createProjectRefsAndExprs, right side call
> int refIdx = offset - 1; // offset = nSysFields + nFields
> List<RelDataTypeField> destFields =
> projChild.getRowType().getFieldList(); // empty
> for (int i = 0; i < nInputRefs; i++) { // nInputRefs = nRightProject = 1
> refIdx = projRefs.nextSetBit(refIdx + 1); // refIdx = nFields
> assert refIdx >= 0;
> final RelDataTypeField destField =
> destFields.get(refIdx - offset); // destFields.get(0) on empty
> list
> ...
> }
> {code}
> The symmetric {{nProject == 0}} case for the left input has the same latent
> issue when {{nSysFields + nFields == 0}}, though I've only encountered the
> right-side variant in practice.
> Zero-column {{Join}} inputs are legitimate. The canonical example is *DEE*
> ({{LogicalValues}} with empty row type and a single empty tuple — the
> multiplicative identity for cross-join), which naturally appears when an
> {{Aggregate}} with {{GROUP BY ()}} has its output mapping pruned to zero
> columns by upstream column pruning.
> ----
> h2. Minimal reproduction
> {code:java}
> @Test void testProjectJoinTransposeWithZeroColumnJoinInput() {
> final RelBuilder builder = RelBuilder.create(config().build());
> final RexBuilder rexBuilder = builder.getRexBuilder();
> final RelDataTypeFactory typeFactory = builder.getTypeFactory();
> // Left: non-empty LogicalValues with one BIGINT column.
> RelDataType intType = typeFactory.createSqlType(SqlTypeName.BIGINT);
> RelNode left = builder
> .values(
> ImmutableList.of(ImmutableList.of((RexLiteral)
> rexBuilder.makeZeroLiteral(intType))),
> typeFactory.builder().add("col1", intType).build())
> .build();
> // Right: DEE — zero-column, one-row LogicalValues (cross-join identity).
> RelNode dee = builder
> .values(ImmutableList.of(ImmutableList.of()),
> typeFactory.builder().build())
> .build();
> // Project(CAST($0 AS VARCHAR)) over Join(inner, true, left, dee).
> // The project must be non-identity, otherwise RelBuilder collapses it away
> // and the rule never fires.
> RelDataType varcharType = typeFactory.createSqlType(SqlTypeName.VARCHAR);
> RelNode root = builder
> .push(left)
> .push(dee)
> .join(JoinRelType.INNER, rexBuilder.makeLiteral(true))
> .project(rexBuilder.makeCast(varcharType, builder.field(0)))
> .build();
> HepPlanner planner = new HepPlanner(
> new HepProgramBuilder()
> .addRuleInstance(CoreRules.PROJECT_JOIN_TRANSPOSE)
> .build());
> planner.setRoot(root);
> planner.findBestExp(); // throws ArrayIndexOutOfBoundsException
> }
> {code}
> The plan that reaches the planner:
> {code}
> LogicalProject(col1=[CAST($0):VARCHAR NOT NULL])
> LogicalJoin(condition=[true], joinType=[inner])
> LogicalValues(tuples=[[{ 0 }]])
> LogicalValues(tuples=[[{ }]])
> {code}
> h3. Current output
> {code}
> java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
> at
> com.google.common.collect.RegularImmutableList.get(RegularImmutableList.java:81)
> at
> org.apache.calcite.rel.rules.PushProjector.createProjectRefsAndExprs(PushProjector.java:523)
> at
> org.apache.calcite.rel.rules.ProjectJoinTransposeRule.onMatch(ProjectJoinTransposeRule.java:117)
> at org.apache.calcite.plan.hep.HepPlanner.applyRule(HepPlanner.java:527)
> ...
> {code}
> h3. Expected output
> The rule either pushes the {{Project}} through the {{Join}} and leaves the
> zero-column side unchanged, or declines to transform (no crash).
> ----
> h2. Proposed fix (or equivalent)
> Guard the Fennel zero-column workaround on the corresponding input having at
> least one field to project. In {{PushProjector.locateAllRefs()}}:
> {code:java}
> if (childRel instanceof Join) {
> if (nRightProject == 0 && rightPreserveExprs.isEmpty()
> && nFieldsRight > 0) { // <-- added guard
> projRefs.set(nFields);
> nRightProject = 1;
> }
> }
> // and analogously for the left-side workaround:
> if (nProject == 0 && childPreserveExprs.isEmpty()
> && (nSysFields + nFields) > 0) { // <-- added guard
> projRefs.set(0);
> nProject = 1;
> }
> {code}
> When the input genuinely has zero fields, there is no "first column" to fall
> back to and the workaround should be skipped. An equivalent fix is to bail
> out of the rule entirely in {{matches()}} when either input's field count is
> zero. The Fennel execution engine referenced in the original comment has been
> removed for some time, so another option is to remove the workaround
> altogether — though that's a broader behavioral change and out of scope for
> the immediate crash.
> ----
> h2. Notes
> * Reproduced on Calcite master at {{95eecd87c}} (a few commits past
> {{1.41.0}}). The bug appears to be long-standing; it's likely present in
> earlier released versions as well.
> * Also reproducible via {{substrait-java}}: an {{Aggregate(GROUP BY (),
> measures)}} with {{Rel.Emit\{outputMapping=[]\}}} yields a DEE on one side of
> a cross when cross-joined into a larger query, tripping this rule during
> optimization in downstream engines.
> * {{ProjectCorrelateTransposeRule}} also constructs a {{PushProjector}}
> ({{ProjectCorrelateTransposeRule.java:79-80}}) and may have the same latent
> issue on a zero-column correlate side — I haven't confirmed.
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