code: @GuardedBy("this")
      private TableSource getTableSource(String databaseName, String tableName)
      {
          checkHoldsLock();
  
          checkReadable();
          Action<TableAndMore> tableAction = tableActions.get(new SchemaTableName(databaseName, tableName));
          if (tableAction == null) {
              return TableSource.PRE_EXISTING_TABLE;
          }
          switch (tableAction.getType()) {
              case ADD:
                  return TableSource.CREATED_IN_THIS_TRANSACTION;
              case ALTER:
                  throw new IllegalStateException("Tables are never altered in the current implementation");
              case DROP:
                  throw new TableNotFoundException(new SchemaTableName(databaseName, tableName));
              case INSERT_EXISTING:
                  return TableSource.PRE_EXISTING_TABLE;
              default:
                  throw new IllegalStateException("Unknown action type");
          }
      }
docs: This method can only be called when the table is known to exist