optimizer: Convert cross joins to hash joins

This commit adds functionality to the optimizer that rewrites cross
joins with equality comparisons filters into hash joins where
appropriate.

Author: mattnibs

compiler/optimizer/join.go

@@ -27,6 +27,83 @@ func replaceJoinWithHashJoin(seq dag.Seq) {
 	})
 }
 
+func liftFilterConvertCrossJoin(seq dag.Seq) dag.Seq {
+	var filter *dag.FilterOp
+	var i int
+	for i = range len(seq) - 3 {
+		var isfilter bool
+		_, isfork := seq[i].(*dag.ForkOp)
+		_, _, _, isjoin := isJoin(seq[i+1])
+		filter, isfilter = seq[i+2].(*dag.FilterOp)
+		if isfork && isjoin && isfilter {
+			break
+		}
+	}
+	if filter == nil {
+		return seq
+	}
+	in := splitPredicate(filter.Expr)
+	var exprs []dag.Expr
+	for _, e := range in {
+		if b, ok := e.(*dag.BinaryExpr); !ok || b.Op != "==" || !convertCrossJoinToHashJoin(seq[i:], b.LHS, b.RHS) {
+			exprs = append(exprs, e)
+		}
+	}
+	if len(exprs) == 0 {
+		seq.Delete(i+2, i+3)
+	} else if len(exprs) != len(in) {
+		seq[i+2] = dag.NewFilterOp(buildConjunction(exprs))
+	}
+	return seq
+}
+
+func convertCrossJoinToHashJoin(seq dag.Seq, lhs, rhs dag.Expr) bool {
+	fork, isfork := seq[0].(*dag.ForkOp)
+	leftAlias, rightAlias, style, isjoin := isJoin(seq[1])
+	if !isfork || !isjoin {
+		return false
+	}
+	if len(fork.Paths) != 2 {
+		panic(fork)
+	}
+	lhsFirst, lok := firstThisPathComponent(lhs)
+	rhsFirst, rok := firstThisPathComponent(rhs)
+	if !lok || !rok {
+		return false
+	}
+	lhs, rhs = dag.CopyExpr(lhs), dag.CopyExpr(rhs)
+	stripFirstThisPathComponent(lhs)
+	stripFirstThisPathComponent(rhs)
+	if lhsFirst == rhsFirst {
+		if lhsFirst == leftAlias {
+			return convertCrossJoinToHashJoin(fork.Paths[0], lhs, rhs)
+		}
+		if lhsFirst == rightAlias {
+			return convertCrossJoinToHashJoin(fork.Paths[1], lhs, rhs)
+		}
+		return false
+	}
+	if style != "cross" {
+		return false
+	}
+	if lhsFirst != leftAlias {
+		lhsFirst, rhsFirst = rhsFirst, lhsFirst
+		lhs, rhs = rhs, lhs
+	}
+	if lhsFirst != leftAlias || rhsFirst != rightAlias {
+		return false
+	}
+	seq[1] = &dag.HashJoinOp{
+		Kind:       "HashJoinOp",
+		Style:      "inner",
+		LeftAlias:  leftAlias,
+		RightAlias: rightAlias,
+		LeftKey:    lhs,
+		RightKey:   rhs,
+	}
+	return true
+}
+
 func equiJoinKeyExprs(e dag.Expr, leftAlias, rightAlias string) (left, right dag.Expr, ok bool) {
 	b, ok := e.(*dag.BinaryExpr)
 	if !ok || b.Op != "==" {

compiler/optimizer/optimizer.go

@@ -144,6 +144,7 @@ func (o *Optimizer) Optimize(main *dag.Main) error {
 	seq = mergeFilters(seq)
 	seq = mergeValuesOps(seq)
 	inlineRecordExprSpreads(seq)
+	seq = liftFilterConvertCrossJoin(seq)
 	seq = joinFilterPullup(seq)
 	seq = removePassOps(seq)
 	seq = replaceSortAndHeadOrTailWithTop(seq)
@@ -511,7 +512,7 @@ func joinFilterPullup(seq dag.Seq) dag.Seq {
 	seq = mergeFilters(seq)
 	for i := 0; i <= len(seq)-3; i++ {
 		fork, isfork := seq[i].(*dag.ForkOp)
-		leftAlias, rightAlias, isjoin := isJoin(seq[i+1])
+		leftAlias, rightAlias, _, isjoin := isJoin(seq[i+1])
 		filter, isfilter := seq[i+2].(*dag.FilterOp)
 		if !isfork || !isjoin || !isfilter {
 			continue
@@ -535,27 +536,31 @@ func joinFilterPullup(seq dag.Seq) dag.Seq {
 			// Filter has been fully pulled up and can be removed.
 			seq.Delete(i+2, i+3)
 		} else {
-			out := remaining[0]
-			for _, e := range remaining[1:] {
-				out = dag.NewBinaryExpr("and", e, out)
-			}
-			seq[i+2] = dag.NewFilterOp(out)
+			seq[i+2] = dag.NewFilterOp(buildConjunction(remaining))
 		}
 		fork.Paths[0] = joinFilterPullup(fork.Paths[0])
 		fork.Paths[1] = joinFilterPullup(fork.Paths[1])
 	}
 	return seq
 }
 
-func isJoin(op dag.Op) (string, string, bool) {
+func isJoin(op dag.Op) (string, string, string, bool) {
 	switch op := op.(type) {
 	case *dag.HashJoinOp:
-		return op.LeftAlias, op.RightAlias, true
+		return op.LeftAlias, op.RightAlias, "inner", true
 	case *dag.JoinOp:
-		return op.LeftAlias, op.RightAlias, true
+		return op.LeftAlias, op.RightAlias, op.Style, true
 	default:
-		return "", "", false
+		return "", "", "", false
+	}
+}
+
+func buildConjunction(exprs []dag.Expr) dag.Expr {
+	out := exprs[0]
+	for _, e := range exprs[1:] {
+		out = dag.NewBinaryExpr("and", e, out)
 	}
+	return out
 }
 
 func splitPredicate(e dag.Expr) []dag.Expr {

compiler/ztests/join-convert-cross.yaml

@@ -0,0 +1,78 @@
+script: |
+  super compile -O -C "
+    fork
+      (
+        values {a1:1}
+      )
+      (
+        fork
+          (
+            values {a2:1}
+          )
+          (
+            values {a3:1} 
+          )
+        | cross join as {left,right}
+      )
+    | cross join as {left,right}
+    | where right.right.a3 == right.left.a2+1
+    | where right.left.a2 == left.a1
+  "
+  echo // ===
+  super compile -O -C "
+    fork
+      (
+        fork
+          (
+            values {a2:1}
+          )
+          (
+            values {a3:1} 
+          )
+        | cross join as {left,right}
+      )
+      (
+        values {a1:1}
+      )
+    | cross join as {left,right}
+    | where left.left.a2 == left.right.a3 and right.a1 == left.left.a2
+  "
+
+outputs:
+  - name: stdout
+    data: |
+      null
+      | fork
+        (
+          values {a1:1}
+        )
+        (
+          fork
+            (
+              values {a2:1}
+            )
+            (
+              values {a3:1}
+            )
+          | inner hashjoin as {left,right} on a2+1==a3
+        )
+      | inner hashjoin as {left,right} on a1==left.a2
+      | output main
+      // ===
+      null
+      | fork
+        (
+          fork
+            (
+              values {a2:1}
+            )
+            (
+              values {a3:1}
+            )
+          | inner hashjoin as {left,right} on a2==a3
+        )
+        (
+          values {a1:1}
+        )
+      | inner hashjoin as {left,right} on left.a2==a1
+      | output main