code: public boolean markDead(Object partitionId, @Nullable Throwable e) {
  		FsClient client = aliveClients.remove(partitionId);
  		if (client != null) {
  			logger.warn("marking " + partitionId + " as dead (" + e + ')');
  			deadClients.put(partitionId, client);
  			return true;
  		}
  		return false;
  	}
docs: Mark partition as dead. It means that no operations will use it and it would not be given to the server selector.
  Next call of {@link #checkDeadPartitions()} or {@link #checkAllPartitions()} will ping this partition and possibly
  mark it as alive again.
  
  @param partitionId id of the partition to be marked
  @param e           optional exception for logging
  @return <code>true</code> if partition was alive and <code>false</code> otherwise