fix: stabilize im server startup and p2p topic scans

server/db/mysql/adapter.go

@@ -996,6 +996,10 @@ func (a *adapter) UpgradeDb() error {
 		return err
 	}
 
+	if err := a.ensureMessageTopicSeqIndex(); err != nil {
+		return err
+	}
+
 	if a.version == adpVersion {
 		return nil
 	}
@@ -1004,6 +1008,22 @@ func (a *adapter) UpgradeDb() error {
 		strconv.Itoa(a.version) + " to " + strconv.Itoa(adpVersion) + " is not supported")
 }
 
+func (a *adapter) ensureMessageTopicSeqIndex() error {
+	const indexName = "messages_topic_seqid"
+	var count int
+	if err := a.db.QueryRow(
+		`SELECT COUNT(*) FROM information_schema.statistics
+		 WHERE table_schema=DATABASE() AND table_name='im_messages' AND index_name=?`,
+		indexName).Scan(&count); err != nil {
+		return err
+	}
+	if count > 0 {
+		return nil
+	}
+	_, err := a.db.Exec("ALTER TABLE im_messages ADD UNIQUE INDEX messages_topic_seqid(topic, seqid)")
+	return err
+}
+
 func createIMNotificationTables(tx *sql.Tx) error {
 	_, err := tx.Exec(
 		`CREATE TABLE im_system_notifications(