Package org.apache.hadoop.hdfs.server.federation.resolver

Interface FileSubclusterResolver

All Known Implementing Classes:

MountTableResolver, MultipleDestinationMountTableResolver

@Private
@Evolving
public interface FileSubclusterResolver

Interface to map a file path in the global name space to a specific subcluster and path in an HDFS name space.

Each path in the global/federated namespace may map to 1-N different HDFS locations. Each location specifies a single nameservice and a single HDFS path. The behavior is similar to MergeFS and Nfly and allows the merger of multiple HDFS locations into a single path. See HADOOP-8298 and HADOOP-12077

For example, a directory listing will fetch listings for each destination path and combine them into a single set of results.

When multiple destinations are available for a path, the destinations are prioritized in a consistent manner. This allows the proxy server to guess the best/most likely destination and attempt it first.

Method Summary

Modifier and Type	Method	Description
java.lang.String	getDefaultNamespace()	Get the default namespace for the cluster.
PathLocation	getDestinationForPath(java.lang.String path)	Get the destinations for a global path.
java.util.List<java.lang.String>	getMountPoints(java.lang.String path)	Get a list of mount points for a path.
static java.util.List<java.lang.String>	getMountPoints(java.lang.String path, java.util.Collection<java.lang.String> mountPoints)	Get a list of mount points for a path.

Method Detail

getDestinationForPath

PathLocation getDestinationForPath(java.lang.String path)
                            throws java.io.IOException

Get the destinations for a global path. Results are from the mount table cache. If multiple destinations are available, the first result is the highest priority destination.

Parameters:

path - Global path.

Returns:

Location in a destination namespace or null if it does not exist.

Throws:

java.io.IOException - Throws exception if the data is not available.

getMountPoints

java.util.List<java.lang.String> getMountPoints(java.lang.String path)
                                         throws java.io.IOException

Get a list of mount points for a path. Results are from the mount table cache.

Parameters:

path - Path to get the mount points under.

Returns:

List of mount points present at this path. Return zero-length list if the path is a mount point but there are no mount points under the path. Return null if the path is not a mount point and there are no mount points under the path.

Throws:

java.io.IOException - Throws exception if the data is not available.

getDefaultNamespace

java.lang.String getDefaultNamespace()

Get the default namespace for the cluster.

Returns:

Default namespace identifier.

getMountPoints

static java.util.List<java.lang.String> getMountPoints(java.lang.String path,
                                                       java.util.Collection<java.lang.String> mountPoints)

Get a list of mount points for a path.

Parameters:

path - Path to get the mount points under.

mountPoints - the mount points to choose.

Returns:

Return empty list if the path is a mount point but there are no mount points under the path. Return null if the path is not a mount point and there are no mount points under the path.