alluxio.client.file.dora

Interface WorkerLocationPolicy

All Known Implementing Classes:

ConsistentHashPolicy, LocalWorkerPolicy

public interface WorkerLocationPolicy

Interface for determining the Alluxio worker location to serve a read or write request. A policy MUST have the property of being deterministic, because distributed clients must be able to resolve the same path to the same worker(s) for the file. Imagine a totally random policy which resolves a path to a random worker in the cluster. The first reader of path /a will resolve to a random worker in the cluster and leave a cache there. A subsequent reader will resolve to another random worker and the chance of a cache-hit is very low! Worse still, that subsequent reader may produce another cache replica. This random policy wastes cache space and provides terrible cache hit rate.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	WorkerLocationPolicy.Factory The factory for the WorkerLocationPolicy.

Method Summary

Modifier and Type	Method and Description
List<BlockWorkerInfo>	getPreferredWorkers(List<BlockWorkerInfo> blockWorkerInfos, String fileId, int count) Find a specified number of workers following the logic defined by the policy.

Method Detail

getPreferredWorkers

List<BlockWorkerInfo> getPreferredWorkers(List<BlockWorkerInfo> blockWorkerInfos,
                                          String fileId,
                                          int count)
                                   throws ResourceExhaustedException

Find a specified number of workers following the logic defined by the policy. This method should return exactly #{count} different workers, no more no less. If the specified number of workers cannot be found, this method will throw a ResourceExhaustedException. We want the semantics here to be explicit when the requirement cannot be satisfied. So the caller should define its own logic handling the exception and finding backups.

Parameters:

blockWorkerInfos -

fileId -

count -

Returns:

a list of preferred workers

Throws:

ResourceExhaustedException - if unable to return exactly #{count} workers