= ShuffleClient

ShuffleClient is the <> of <> that can <>.

ShuffleClient can optionally be <> with an appId (that actually does nothing by default)

ShuffleClient has <> that are used when BlockManager is requested for a storage:BlockManager.md#shuffleMetricsSource[shuffle-related Spark metrics source] (only when Executor is executor:Executor.md#creating-instance[created] for a non-local / cluster mode).

[[contract]] [source, java]

package org.apache.spark.network.shuffle;

abstract class ShuffleClient implements Closeable { // only required methods that have no implementation // the others follow abstract void fetchBlocks( String host, int port, String execId, String[] blockIds, BlockFetchingListener listener, TempFileManager tempFileManager); }

.(Subset of) ShuffleClient Contract [cols="1,2",options="header",width="100%"] |=== | Method | Description

| fetchBlocks | [[fetchBlocks]] Fetches a sequence of blocks from a remote block manager node asynchronously

Used exclusively when ShuffleBlockFetcherIterator is requested to storage:ShuffleBlockFetcherIterator.md#sendRequest[sendRequest] |===

[[implementations]] .ShuffleClients [cols="1,2",options="header",width="100%"] |=== | ShuffleClient | Description

| storage:BlockTransferService.md[] | [[BlockTransferService]]

| storage:ExternalShuffleClient.md[] | [[ExternalShuffleClient]] |===

== [[init]] init Method

[source, java]¶

void init( String appId)

init does nothing by default.

[NOTE]¶

init is used when:

• BlockManager is requested to storage:BlockManager.md#initialize[initialize]

* Spark on Mesos' MesosCoarseGrainedSchedulerBackend is requested to registered¶

== [[shuffleMetrics]] Shuffle Metrics

[source, java]¶

MetricSet shuffleMetrics()¶

shuffleMetrics returns an empty Dropwizard Metrics' https://metrics.dropwizard.io/3.1.0/apidocs/com/codahale/metrics/MetricSet.html[MetricSet] by default.

NOTE: shuffleMetrics is used exclusively when BlockManager is requested for a storage:BlockManager.md#shuffleMetricsSource[shuffle-related Spark metrics source] (only when Executor is executor:Executor.md#creating-instance[created] for a non-local / cluster mode).