src/Pure/Thy/sessions.scala

 
     def read_theories(db: SQL.Database, name: String): List[String] =
       read_theory_timings(db, name).flatMap(Markup.Name.unapply)
 
     def read_errors(db: SQL.Database, name: String): List[String] =
-      Build_Log.uncompress_errors(read_bytes(db, name, Session_Info.errors), cache = cache.xz)
+      Build_Log.uncompress_errors(read_bytes(db, name, Session_Info.errors), cache = cache)
 
     def read_build(db: SQL.Database, name: String): Option[Build.Session_Info] =
     {
       if (db.tables.contains(Session_Info.table.name)) {
         db.using_statement(Session_Info.table.select(Session_Info.build_columns,