org.apache.hadoop.net
Class CachedDNSToSwitchMapping

java.lang.Object
  org.apache.hadoop.net.AbstractDNSToSwitchMapping
      org.apache.hadoop.net.CachedDNSToSwitchMapping

All Implemented Interfaces:

Configurable, DNSToSwitchMapping

Direct Known Subclasses:

ScriptBasedMapping

@InterfaceAudience.Public
@InterfaceStability.Evolving
public class CachedDNSToSwitchMapping
extends AbstractDNSToSwitchMapping

A cached implementation of DNSToSwitchMapping that takes an raw DNSToSwitchMapping and stores the resolved network location in a cache. The following calls to a resolved network location will get its location from the cache.

Field Summary

protected DNSToSwitchMapping

rawMapping The uncached mapping

Constructor Summary

CachedDNSToSwitchMapping(DNSToSwitchMapping rawMapping)
cache a raw DNS mapping

Method Summary

boolean	isSingleSwitch() Delegate the switch topology query to the raw mapping, via AbstractDNSToSwitchMapping.isMappingSingleSwitch(DNSToSwitchMapping)
List<String>	resolve(List<String> names) Resolves a list of DNS-names/IP-addresses and returns back a list of switch information (network paths).

Methods inherited from class org.apache.hadoop.net.AbstractDNSToSwitchMapping

getConf, isMappingSingleSwitch, setConf

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

rawMapping

protected final DNSToSwitchMapping rawMapping

The uncached mapping

Constructor Detail

CachedDNSToSwitchMapping

public CachedDNSToSwitchMapping(DNSToSwitchMapping rawMapping)

cache a raw DNS mapping

Parameters:

rawMapping - the raw mapping to cache

Method Detail

resolve

public List<String> resolve(List<String> names)

Description copied from interface: DNSToSwitchMapping

Resolves a list of DNS-names/IP-addresses and returns back a list of switch information (network paths). One-to-one correspondence must be maintained between the elements in the lists. Consider an element in the argument list - x.y.com. The switch information that is returned must be a network path of the form /foo/rack, where / is the root, and 'foo' is the switch where 'rack' is connected. Note the hostname/ip-address is not part of the returned path. The network topology of the cluster would determine the number of components in the network path.

If a name cannot be resolved to a rack, the implementation should return NetworkTopology.DEFAULT_RACK. This is what the bundled implementations do, though it is not a formal requirement

Parameters:

names - the list of hosts to resolve (can be empty)

Returns:

list of resolved network paths. If names is empty, the returned list is also empty

isSingleSwitch

public boolean isSingleSwitch()

Delegate the switch topology query to the raw mapping, via AbstractDNSToSwitchMapping.isMappingSingleSwitch(DNSToSwitchMapping)

Overrides:

isSingleSwitch in class AbstractDNSToSwitchMapping

Returns:

true iff the raw mapper is considered single-switch.