Package org.apache.hadoop.net

Interface DNSToSwitchMappingWithDependency

All Superinterfaces:

DNSToSwitchMapping

All Known Implementing Classes:

ScriptBasedMappingWithDependency

@Private
@Evolving
public interface DNSToSwitchMappingWithDependency
extends DNSToSwitchMapping

An interface that must be implemented to allow pluggable DNS-name/IP-address to RackID resolvers.

Method Summary

Modifier and Type	Method	Description
java.util.List<java.lang.String>	getDependency(java.lang.String name)	Get a list of dependent DNS-names for a given DNS-name/IP-address.

Methods inherited from interface org.apache.hadoop.net.DNSToSwitchMapping

reloadCachedMappings, reloadCachedMappings, resolve

Method Detail

getDependency

java.util.List<java.lang.String> getDependency(java.lang.String name)

Get a list of dependent DNS-names for a given DNS-name/IP-address. Dependent DNS-names fall into the same fault domain which must be taken into account when placing replicas. This is intended to be used for cross node group dependencies when node groups are not sufficient to distinguish data nodes by fault domains. In practice, this is needed when a compute server runs VMs which use shared storage (as opposite to directly attached storage). In this case data nodes fall in two different fault domains. One fault domain is defined by a compute server and the other is defined by storage. With node groups we can group data nodes either by server fault domain or by storage fault domain. However one of the fault domains cannot be handled and there we need to define cross node group dependencies. These dependencies are applied in block placement polices which ensure that no two replicas will be on two dependent nodes.

Parameters:

name - - host name or IP address of a data node. Input host name parameter must take a value of dfs.datanode.hostname config value if this config property is set. Otherwise FQDN of the data node is used.

Returns:

list of dependent host names. If dfs.datanode.hostname config property is set, then its value must be returned. Otherwise, FQDN is returned.