Merge #56161

56161: sql: add support for joinReader to be the first join in paired joins r=sumeerbhola a=sumeerbhola

This is to allow lookup joins to be used for left outer/semi/anti
joins with non-covering indexes. Currently only semi joins for
this case can use the index (by doing two inner joins and a DistinctOn)

Paired joins with a non-covering index will be used as follows:
- Left outer join: will become a pair of left outer lookup joins.
- Left anti join: will be a left outer lookup join followed by
  a left anti lookup join.
- Left semi join: will be an inner lookup join followed by a
  left semi lookup join.

This PR does not contain the optimizer changes.

Informs #55452

Release note: None

Co-authored-by: sumeerbhola <sumeer@cockroachlabs.com>

pkg/sql/execinfra/version.go

@@ -39,7 +39,7 @@ import "github.com/cockroachdb/cockroach/pkg/sql/execinfrapb"
 //
 // ATTENTION: When updating these fields, add a brief description of what
 // changed to the version history below.
-const Version execinfrapb.DistSQLVersion = 40
+const Version execinfrapb.DistSQLVersion = 41
 
 // MinAcceptedVersion is the oldest version that the server is compatible with.
 // A server will not accept flows with older versions.
@@ -51,6 +51,11 @@ const MinAcceptedVersion execinfrapb.DistSQLVersion = 40
 
 Please add new entries at the top.
 
+- Version: 41 (MinAcceptedVersion: 40)
+  - A paired joiner approach for lookup joins was added, for left
+    outer/semi/anti joins involving a pair of joinReaders, where the
+    first join uses a non-covering index.
+
 - Version: 40 (MinAcceptedVersion: 40)
   - A new field was added execinfrapb.ProcessorSpec to propagate the result
     column types of a processor. This change is not backwards compatible
@@ -62,7 +67,7 @@ Please add new entries at the top.
     protobuf struct for easier propagation to the remote nodes during the
     execution.
 
-- Version: 38 (MinAcceptedVersion: 38)
+- Version: 38 (MinAcceptedVersion: 37)
   - A paired joiner approach for inverted joins was added, for left
     outer/semi/anti joins involving the invertedJoiner and joinReader.
 

pkg/sql/execinfrapb/processors_sql.proto

@@ -243,6 +243,11 @@ message IndexSkipTableReaderSpec {
 // The output for LEFT_SEMI:
 // a2, b1, c1, d4, true
 // Again, the d, cont columns will be projected away after the join.
+//
+// The example above is for a lookup join as the second join in the
+// paired-joins. The lookup join can also be the first join in the
+// paired-joins, which is indicated by both
+// OutputGroupContinuationForLeftRow and MaintainOrdering set to true.
 message JoinReaderSpec {
   optional sqlbase.TableDescriptor table = 1 [(gogoproto.nullable) = false];
 
@@ -314,8 +319,16 @@ message JoinReaderSpec {
   optional bool has_system_columns = 13 [(gogoproto.nullable) = false];
 
   // LeftJoinWithPairedJoiner is used when a left {outer,anti,semi} join is
-  // being achieved by pairing two joins. See the comment above.
+  // being achieved by pairing two joins, and this is the second join. See
+  // the comment above.
   optional bool left_join_with_paired_joiner = 14 [(gogoproto.nullable) = false];
+
+  // OutputGroupContinuationForLeftRow indicates that this join is the first
+  // join in the paired-joins. At most one of OutputGroupContinuationForLeftRow
+  // and LeftJoinWithPairedJoiner must be true. Additionally, if
+  // OutputGroupContinuationForLeftRow is true, MaintainOrdering must also
+  // be true.
+  optional bool output_group_continuation_for_left_row = 15 [(gogoproto.nullable) = false];
 }
 
 // SorterSpec is the specification for a "sorting aggregator". A sorting

pkg/sql/rowexec/hashjoiner.go

@@ -158,6 +158,7 @@ func newHashJoiner(
 		spec.OnExpr,
 		spec.LeftEqColumns,
 		spec.RightEqColumns,
+		false, /* outputContinuationColumn */
 		post,
 		output,
 		execinfra.ProcStateOpts{

pkg/sql/rowexec/joinerbase.go

@@ -50,6 +50,7 @@ func (jb *joinerBase) init(
 	onExpr execinfrapb.Expression,
 	leftEqColumns []uint32,
 	rightEqColumns []uint32,
+	outputContinuationColumn bool,
 	post *execinfrapb.PostProcessSpec,
 	output execinfra.RowReceiver,
 	opts execinfra.ProcStateOpts,
@@ -74,18 +75,26 @@ func (jb *joinerBase) init(
 	jb.eqCols[leftSide] = leftEqColumns
 	jb.eqCols[rightSide] = rightEqColumns
 
-	size := len(leftTypes) + len(rightTypes)
-	jb.combinedRow = make(rowenc.EncDatumRow, size)
+	rowSize := len(leftTypes) + len(rightTypes)
+	if outputContinuationColumn {
+		// NB: Can only be true for inner joins and left outer joins.
+		rowSize++
+	}
+	jb.combinedRow = make(rowenc.EncDatumRow, rowSize)
 
-	condTypes := make([]*types.T, 0, size)
+	// condTypes does not include the continuation column, but the slice has the
+	// capacity for it, since outputTypes later adds the continuation column.
+	condTypes := make([]*types.T, 0, rowSize)
 	condTypes = append(condTypes, leftTypes...)
 	condTypes = append(condTypes, rightTypes...)
 
-	outputSize := len(leftTypes)
-	if jb.joinType.ShouldIncludeRightColsInOutput() {
-		outputSize += len(rightTypes)
+	outputTypes := condTypes
+	// NB: outputContinuationCol implies jb.joinType.ShouldIncludeRightColsInOutput()
+	if !jb.joinType.ShouldIncludeRightColsInOutput() {
+		outputTypes = outputTypes[:len(leftTypes)]
+	} else if outputContinuationColumn {
+		outputTypes = append(outputTypes, types.Bool)
 	}
-	outputTypes := condTypes[:outputSize]
 
 	if err := jb.ProcessorBase.Init(
 		self, post, outputTypes, flowCtx, processorID, output, nil /* memMonitor */, opts,
@@ -119,7 +128,9 @@ func (j joinSide) String() string {
 }
 
 // renderUnmatchedRow creates a result row given an unmatched row on either
-// side. Only used for outer joins.
+// side. Only used for outer joins. Note that if the join is outputting a
+// continuation column, the returned slice does not include the continuation
+// column, but has the capacity for it.
 func (jb *joinerBase) renderUnmatchedRow(row rowenc.EncDatumRow, side joinSide) rowenc.EncDatumRow {
 	lrow, rrow := jb.emptyLeft, jb.emptyRight
 	if side == leftSide {
@@ -158,7 +169,9 @@ func shouldEmitUnmatchedRow(side joinSide, joinType descpb.JoinType) bool {
 }
 
 // render constructs a row with columns from both sides. The ON condition is
-// evaluated; if it fails, returns nil.
+// evaluated; if it fails, returns nil. Note that if the join is outputting a
+// continuation column, the returned slice does not include the continuation
+// column, but has the capacity for it.
 func (jb *joinerBase) render(lrow, rrow rowenc.EncDatumRow) (rowenc.EncDatumRow, error) {
 	jb.combinedRow = jb.combinedRow[:len(lrow)+len(rrow)]
 	copy(jb.combinedRow, lrow)

pkg/sql/rowexec/joinreader.go

@@ -110,26 +110,26 @@ type joinReader struct {
 	// (or evaluate it accurately, as is sometimes the case with inverted
 	// indexes). The first join is running a left outer or inner join, and each
 	// group of rows seen by the second join correspond to one left row.
-	//
-	// TODO(sumeer): add support for joinReader to also be the first
-	// join in this pair, say when the index can evaluate most of the
-	// join condition (the part with low selectivity), but not all.
-	// Currently only the invertedJoiner can serve as the first join
-	// in the pair.
 
 	// The input rows in the current batch belong to groups which are tracked in
 	// groupingState. The last row from the last batch is in
 	// lastInputRowFromLastBatch -- it is tracked because we don't know if it
 	// was the last row in a group until we get to the next batch. NB:
 	// groupingState is used even when there is no grouping -- we simply have
-	// groups of one.
+	// groups of one. The no grouping cases include the case of this join being
+	// the first join in the paired joins.
 	groupingState *inputBatchGroupingState
 
 	lastBatchState struct {
 		lastInputRow       rowenc.EncDatumRow
 		lastGroupMatched   bool
 		lastGroupContinued bool
 	}
+
+	// Set to true when this is the first join in the paired-joins (see the
+	// detailed comment in the spec). This can never be true for index joins,
+	// and requires that the spec has MaintainOrdering set to true.
+	outputGroupContinuationForLeftRow bool
 }
 
 var _ execinfra.Processor = &joinReader{}
@@ -153,6 +153,10 @@ func newJoinReader(
 	if spec.IndexIdx != 0 && readerType == indexJoinReaderType {
 		return nil, errors.AssertionFailedf("index join must be against primary index")
 	}
+	if spec.OutputGroupContinuationForLeftRow && !spec.MaintainOrdering {
+		return nil, errors.AssertionFailedf(
+			"lookup join must maintain ordering since it is first join in paired-joins")
+	}
 
 	var lookupCols []uint32
 	switch readerType {
@@ -168,15 +172,14 @@ func newJoinReader(
 		return nil, errors.Errorf("unsupported joinReaderType")
 	}
 	jr := &joinReader{
-		desc:             tabledesc.MakeImmutable(spec.Table),
-		maintainOrdering: spec.MaintainOrdering,
-		input:            input,
-		inputTypes:       input.OutputTypes(),
-		lookupCols:       lookupCols,
+		desc:                              tabledesc.MakeImmutable(spec.Table),
+		maintainOrdering:                  spec.MaintainOrdering,
+		input:                             input,
+		inputTypes:                        input.OutputTypes(),
+		lookupCols:                        lookupCols,
+		outputGroupContinuationForLeftRow: spec.OutputGroupContinuationForLeftRow,
 	}
 	if readerType != indexJoinReaderType {
-		// TODO(sumeer): When LeftJoinWithPairedJoiner, the lookup columns and the
-		// bool column must be projected away by the optimizer after this join.
 		jr.groupingState = &inputBatchGroupingState{doGrouping: spec.LeftJoinWithPairedJoiner}
 	}
 	var err error
@@ -239,6 +242,7 @@ func newJoinReader(
 		spec.OnExpr,
 		leftEqCols,
 		indexCols,
+		spec.OutputGroupContinuationForLeftRow,
 		post,
 		output,
 		execinfra.ProcStateOpts{
@@ -361,11 +365,12 @@ func (jr *joinReader) initJoinReaderStrategy(
 		drc.DisableCache = true
 	}
 	jr.strategy = &joinReaderOrderingStrategy{
-		joinerBase:           &jr.joinerBase,
-		defaultSpanGenerator: spanGenerator,
-		isPartialJoin:        jr.joinType == descpb.LeftSemiJoin || jr.joinType == descpb.LeftAntiJoin,
-		lookedUpRows:         drc,
-		groupingState:        jr.groupingState,
+		joinerBase:                        &jr.joinerBase,
+		defaultSpanGenerator:              spanGenerator,
+		isPartialJoin:                     jr.joinType == descpb.LeftSemiJoin || jr.joinType == descpb.LeftAntiJoin,
+		lookedUpRows:                      drc,
+		groupingState:                     jr.groupingState,
+		outputGroupContinuationForLeftRow: jr.outputGroupContinuationForLeftRow,
 	}
 }
 
@@ -404,8 +409,14 @@ func (jr *joinReader) neededRightCols() util.FastIntSet {
 	// Get the columns from the right side of the join and shift them over by
 	// the size of the left side so the right side starts at 0.
 	neededRightCols := util.MakeFastIntSet()
+	var lastCol int
 	for i, ok := neededCols.Next(len(jr.inputTypes)); ok; i, ok = neededCols.Next(i + 1) {
-		neededRightCols.Add(i - len(jr.inputTypes))
+		lastCol = i - len(jr.inputTypes)
+		neededRightCols.Add(lastCol)
+	}
+	if jr.outputGroupContinuationForLeftRow {
+		// The lastCol is the bool continuation column and not a right column.
+		neededRightCols.Remove(lastCol)
 	}
 
 	// Add columns needed by OnExpr.
@@ -580,7 +591,7 @@ func (jr *joinReader) performLookup() (joinReaderState, *execinfrapb.ProducerMet
 			}
 		}
 
-		// Fetch the next row and copy it into the row container.
+		// Fetch the next row and tell the strategy to process it.
 		lookedUpRow, _, _, err := jr.fetcher.NextRow(jr.Ctx)
 		if err != nil {
 			jr.MoveToDraining(scrub.UnwrapScrubError(err))
@@ -868,12 +879,16 @@ func (ib *inputBatchGroupingState) setFirstGroupMatched() {
 	ib.groupState[0].matched = true
 }
 
-func (ib *inputBatchGroupingState) setMatched(rowIndex int) {
+// setMatched records that the given rowIndex has matched. It returns the
+// previous value of the matched field.
+func (ib *inputBatchGroupingState) setMatched(rowIndex int) bool {
 	groupIndex := rowIndex
 	if ib.doGrouping {
 		groupIndex = ib.batchRowToGroupIndex[rowIndex]
 	}
+	rv := ib.groupState[groupIndex].matched
 	ib.groupState[groupIndex].matched = true
+	return rv
 }
 
 func (ib *inputBatchGroupingState) getMatched(rowIndex int) bool {

pkg/sql/rowexec/joinreader_strategies.go

@@ -390,6 +390,12 @@ type joinReaderOrderingStrategy struct {
 	}
 
 	groupingState *inputBatchGroupingState
+
+	// outputGroupContinuationForLeftRow is true when this join is the first
+	// join in paired-joins. Note that in this case the input batches will
+	// always be of size 1 (real input batching only happens when this join is
+	// the second join in paired-joins).
+	outputGroupContinuationForLeftRow bool
 }
 
 func (s *joinReaderOrderingStrategy) getLookupRowsBatchSizeHint() int64 {
@@ -445,7 +451,8 @@ func (s *joinReaderOrderingStrategy) processLookedUpRow(
 		// During a SemiJoin or AntiJoin, we only output if we've seen no match
 		// for this input row yet. Additionally, since we don't have to render
 		// anything to output a Semi or Anti join match, we can evaluate our
-		// on condition now.
+		// on condition now. NB: the first join in paired-joins is never a
+		// SemiJoin or AntiJoin.
 		if !s.groupingState.getMatched(inputRowIdx) {
 			renderedRow, err := s.render(s.inputRows[inputRowIdx], row)
 			if err != nil {
@@ -500,6 +507,10 @@ func (s *joinReaderOrderingStrategy) nextRowToEmit(
 				// An outer-join non-match means we emit the input row with NULLs for
 				// the right side.
 				if renderedRow := s.renderUnmatchedRow(inputRow, leftSide); renderedRow != nil {
+					if s.outputGroupContinuationForLeftRow {
+						// This must be the first row being output for this input row.
+						renderedRow = append(renderedRow, falseEncDatum)
+					}
 					return renderedRow, jrEmittingRows, nil
 				}
 			case descpb.LeftAntiJoin:
@@ -532,7 +543,16 @@ func (s *joinReaderOrderingStrategy) nextRowToEmit(
 		return nil, jrStateUnknown, err
 	}
 	if outputRow != nil {
-		s.groupingState.setMatched(s.emitCursor.inputRowIdx)
+		wasAlreadyMatched := s.groupingState.setMatched(s.emitCursor.inputRowIdx)
+		if s.outputGroupContinuationForLeftRow {
+			if wasAlreadyMatched {
+				// Not the first row output for this input row.
+				outputRow = append(outputRow, trueEncDatum)
+			} else {
+				// First row output for this input row.
+				outputRow = append(outputRow, falseEncDatum)
+			}
+		}
 	}
 	return outputRow, jrEmittingRows, nil
 }