For large joins, prefer sticking to the user-supplied join order over full enumeration.

enginetest/memory_engine_test.go

@@ -426,7 +426,6 @@ func TestIntegrationQueryPlans(t *testing.T) {
 }
 
 func TestImdbQueryPlans(t *testing.T) {
-	t.Skip("tests are too slow")
 	harness := enginetest.NewMemoryHarness("nativeIndexes", 1, nil)
 	enginetest.TestImdbPlans(t, harness)
 }

enginetest/scriptgen/setup/scripts/imdb

@@ -306,62 +306,79 @@ create index role_id_cast_info on cast_info(role_id);
 exec
 analyze table aka_name update histogram on id using data '{"row_count": 900662}';
 ----
+
 exec
 analyze table aka_title update histogram on id using data '{"row_count": 361376}';
 ----
+
 exec
 analyze table cast_info update histogram on id using data '{"row_count": 36124530}';
 ----
+
 exec
 analyze table char_name update histogram on id using data '{"row_count": 3136382}';
 ----
+
 exec
 analyze table company_name update histogram on id using data '{"row_count": 234825}';
 ----
+
 exec
 analyze table company_type update histogram on id using data '{"row_count": 4}';
 ----
+
 exec
 analyze table complete_cast update histogram on id using data '{"row_count": 135086}';
 ----
+
 exec
 analyze table comp_cast_type update histogram on id using data '{"row_count": 4}';
 ----
+
 exec
 analyze table info_type update histogram on id using data '{"row_count": 113}';
 ----
+
 exec
 analyze table keyword update histogram on id using data '{"row_count": 134110}';
 ----
+
 exec
 analyze table kind_type update histogram on id using data '{"row_count": 7}';
 ----
+
 exec
 analyze table link_type update histogram on id using data '{"row_count": 18}';
 ----
+
 exec
 analyze table movie_companies update histogram on id using data '{"row_count": 2604067}';
 ----
+
 exec
 analyze table movie_info update histogram on id using data '{"row_count": 14355706}';
 ----
+
 exec
 analyze table movie_info_idx update histogram on id using data '{"row_count": 1380035}';
 ----
+
 exec
 analyze table movie_keyword update histogram on id using data '{"row_count": 4523930}';
 ----
+
 exec
 analyze table movie_link update histogram on id using data '{"row_count": 29997}';
 ----
+
 exec
 analyze table name update histogram on id using data '{"row_count": 4167453}';
 ----
+
 exec
 analyze table person_info update histogram on id using data '{"row_count": 2024951}';
 ----
+
 exec
-analyze table row_type update histogram on id using data '{"row_count": 12}';
-----
 analyze table title update histogram on id using data '{"row_count": 2527799}';
 ----

sql/memo/expr_group.go

@@ -18,7 +18,6 @@ import (
 	"fmt"
 	"io"
 	"iter"
-	"maps"
 	"slices"
 	"sort"
 	"strings"
@@ -95,14 +94,18 @@ func (e *ExprGroup) Iter() iter.Seq[RelExpr] {
 
 // children returns a unioned list of child ExprGroup for
 // every logical plan in this group.
-func (e *ExprGroup) children() iter.Seq[*ExprGroup] {
+func (e *ExprGroup) children(yield func(group *ExprGroup) bool) {
 	children := make(map[GroupId]*ExprGroup)
 	for n := range e.Iter() {
 		for _, n := range n.Children() {
-			children[n.Id] = n
+			if _, exists := children[n.Id]; !exists {
+				children[n.Id] = n
+				if !yield(n) {
+					return
+				}
+			}
 		}
 	}
-	return maps.Values(children)
 }
 
 // updateBest updates a group's Best to the given expression if the cost is lower than the current best.

sql/memo/join_order_builder.go

@@ -181,7 +181,8 @@ func (j *joinOrderBuilder) ReorderJoin(n sql.Node) {
 			j.m.Tracer.Log("Successfully built single lookup plan")
 			return
 		}
-		j.m.Tracer.Log("Failed to build single lookup plan, falling back to exhaustive enumeration")
+		j.m.Tracer.Log("Failed to identify an ideal join plan, exhaustive enumeration would be too slow, so preserve the join order in the original query")
+		return
 	} else if j.hasCrossJoin {
 		j.m.Tracer.Log("Join contains cross joins, attempting single lookup plan first")
 		// Rely on FastReorder to avoid plans that drop filters with cross joins

sql/memo/memo.go

@@ -629,7 +629,7 @@ func (m *Memo) String() string {
 				continue
 			}
 			exprs[int(TableIdForSource(g.Id))] = g.String()
-			newGroups = slices.AppendSeq(newGroups, g.children())
+			newGroups = slices.AppendSeq(newGroups, g.children)
 		}
 		groups = newGroups
 	}
@@ -678,7 +678,7 @@ func (m *Memo) LogCostDebugString() {
 			}
 
 			exprs[int(TableIdForSource(g.Id))] = g.CostTreeString(prefix)
-			newGroups = slices.AppendSeq(newGroups, g.children())
+			newGroups = slices.AppendSeq(newGroups, g.children)
 		}
 		groups = newGroups
 	}

sql/memo/rel_props.go

@@ -323,7 +323,7 @@ func (m *Memo) CardMemoGroups(ctx *sql.Context, g *ExprGroup) {
 	if g.RelProps.stat != nil {
 		return
 	}
-	for g := range g.children() {
+	for g := range g.children {
 		m.CardMemoGroups(ctx, g)
 	}
 	s := m.statsForRel(ctx, g.First)

sql/memo/select_hints.go

@@ -199,7 +199,7 @@ func (o joinOrderHint) build(grp *ExprGroup) {
 	}
 	o.groups[grp.Id] = s
 
-	for g := range grp.children() {
+	for g := range grp.children {
 		if _, ok := o.groups[g.Id]; !ok {
 			// avoid duplicate work
 			o.build(g)