perf(stats): simplify username lookup index

internal/modules/stats/startup.go

@@ -14,7 +14,14 @@ import (
 	"github.com/tiennm99/miti99bot/internal/systemstate"
 )
 
-const miscCommandRenameMigrationName = "stats-command-renames-misc-20260701"
+const (
+	miscCommandRenameMigrationName = "stats-command-renames-misc-20260701"
+
+	statsCommandUsersIndexName      = "stats_cmd_n_user"
+	statsUserCommandsIndexName      = "stats_uid_n_cmd"
+	statsUsernameLookupIndexName    = "stats_user_uid"
+	statsLegacyUserUpdatedIndexName = "stats_user_updated_at"
+)
 
 type commandRename struct {
 	old string
@@ -34,6 +41,9 @@ func InitStore(ctx context.Context, statsColl, systemColl storage.Collection) er
 		if err := ensureUsageIndexes(ctx, mongoColl); err != nil {
 			return err
 		}
+		if err := dropIndexIfExists(ctx, mongoColl, statsLegacyUserUpdatedIndexName); err != nil {
+			return err
+		}
 	}
 	if err := runMiscCommandRenameMigration(ctx, statsColl, systemColl); err != nil {
 		return err
@@ -130,15 +140,15 @@ func ensureUsageIndexes(ctx context.Context, coll *mongo.Collection) error {
 	models := []mongo.IndexModel{
 		{
 			Keys:    bson.D{bsonField("cmd", 1), bsonField("n", -1), bsonField("user", 1)},
-			Options: options.Index().SetName("stats_cmd_n_user"),
+			Options: options.Index().SetName(statsCommandUsersIndexName),
 		},
 		{
 			Keys:    bson.D{bsonField("uid", 1), bsonField("n", -1), bsonField("cmd", 1)},
-			Options: options.Index().SetName("stats_uid_n_cmd"),
+			Options: options.Index().SetName(statsUserCommandsIndexName),
 		},
 		{
-			Keys:    bson.D{bsonField("user", 1), bsonField("updatedAt", -1)},
-			Options: options.Index().SetName("stats_user_updated_at"),
+			Keys:    bson.D{bsonField("user", 1), bsonField("uid", 1)},
+			Options: options.Index().SetName(statsUsernameLookupIndexName),
 		},
 	}
 	if _, err := coll.Indexes().CreateMany(ctx, models); err != nil {
@@ -146,3 +156,31 @@ func ensureUsageIndexes(ctx context.Context, coll *mongo.Collection) error {
 	}
 	return nil
 }
+
+func dropIndexIfExists(ctx context.Context, coll *mongo.Collection, name string) error {
+	cur, err := coll.Indexes().List(ctx)
+	if err != nil {
+		return fmt.Errorf("stats list indexes before drop %s: %w", name, err)
+	}
+	defer func() { _ = cur.Close(ctx) }()
+
+	for cur.Next(ctx) {
+		var doc struct {
+			Name string `bson:"name"`
+		}
+		if err := cur.Decode(&doc); err != nil {
+			return fmt.Errorf("stats decode index before drop %s: %w", name, err)
+		}
+		if doc.Name != name {
+			continue
+		}
+		if err := coll.Indexes().DropOne(ctx, name); err != nil {
+			return fmt.Errorf("stats drop legacy index %s: %w", name, err)
+		}
+		return nil
+	}
+	if err := cur.Err(); err != nil {
+		return fmt.Errorf("stats index cursor before drop %s: %w", name, err)
+	}
+	return nil
+}

internal/modules/stats/startup_mongo_test.go

@@ -7,6 +7,10 @@ import (
 	"testing"
 	"time"
 
+	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.mongodb.org/mongo-driver/v2/mongo"
+	"go.mongodb.org/mongo-driver/v2/mongo/options"
+
 	"github.com/tiennm99/miti99bot/internal/storage"
 )
 
@@ -36,14 +40,24 @@ func TestInitStore_MongoCreatesIndexes(t *testing.T) {
 	statsColl := provider.Collection("stats")
 	systemColl := provider.Collection("system")
 
-	if err := InitStore(ctx, statsColl, systemColl); err != nil {
-		t.Fatalf("InitStore: %v", err)
-	}
-
 	rawStatsColl, ok := storage.MongoCollection(statsColl)
 	if !ok {
 		t.Fatal("stats collection is not Mongo-backed")
 	}
+	if _, err := rawStatsColl.Indexes().CreateOne(ctx, mongo.IndexModel{
+		Keys:    bson.D{bsonField("user", 1), bsonField("updatedAt", -1)},
+		Options: options.Index().SetName(statsLegacyUserUpdatedIndexName),
+	}); err != nil {
+		t.Fatalf("seed legacy index: %v", err)
+	}
+
+	if err := InitStore(ctx, statsColl, systemColl); err != nil {
+		t.Fatalf("InitStore: %v", err)
+	}
+	if err := InitStore(ctx, statsColl, systemColl); err != nil {
+		t.Fatalf("InitStore second run: %v", err)
+	}
+
 	cur, err := rawStatsColl.Indexes().List(ctx)
 	if err != nil {
 		t.Fatalf("list indexes: %v", err)
@@ -63,9 +77,12 @@ func TestInitStore_MongoCreatesIndexes(t *testing.T) {
 	if err := cur.Err(); err != nil {
 		t.Fatalf("index cursor: %v", err)
 	}
-	for _, name := range []string{"stats_cmd_n_user", "stats_uid_n_cmd", "stats_user_updated_at"} {
+	for _, name := range []string{statsCommandUsersIndexName, statsUserCommandsIndexName, statsUsernameLookupIndexName} {
 		if !found[name] {
 			t.Fatalf("missing index %s; indexes=%v", name, found)
 		}
 	}
+	if found[statsLegacyUserUpdatedIndexName] {
+		t.Fatalf("legacy index %s was not dropped; indexes=%v", statsLegacyUserUpdatedIndexName, found)
+	}
 }

internal/modules/stats/usage_store.go

@@ -439,8 +439,7 @@ func (s *mongoUsageStore) userIDByUsername(ctx context.Context, username string)
 			"deleted": bson.M{"$ne": true},
 		},
 		options.FindOne().
-			SetProjection(bson.M{"uid": 1}).
-			SetSort(bson.D{bsonField("updatedAt", -1)}),
+			SetProjection(bson.M{"uid": 1}),
 	).Decode(&doc)
 	if err != nil {
 		if errors.Is(err, mongo.ErrNoDocuments) {