public void splitLog(final ServerName serverName) throws IOException {
    splitLog(Collections.<ServerName> singleton(serverName));
  }
Inspect the log directory to find dead servers which need recovery work
@return A set of ServerNames which aren't running but still have WAL files left in file system
@deprecated With proc-v2, we can record the crash server with procedure store, so do not need
            to scan the wal directory to find out the splitting wal directory any more. Leave
            it here only because {@code RecoverMetaProcedure}(which is also deprecated) uses
            it.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterWalManager.java