[SPARK-24355] Spark external shuffle server improvement to better handle block fetch requests. #22173
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one or more | ||
| * contributor license agreements. See the NOTICE file distributed with | ||
| * this work for additional information regarding copyright ownership. | ||
| * The ASF licenses this file to You under the Apache License, Version 2.0 | ||
| * (the "License"); you may not use this file except in compliance with | ||
| * the License. You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
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| package org.apache.spark.network.server; | ||
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| import java.net.SocketAddress; | ||
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| import com.google.common.base.Throwables; | ||
| import io.netty.channel.Channel; | ||
| import io.netty.channel.ChannelFuture; | ||
| import io.netty.channel.ChannelFutureListener; | ||
| import io.netty.channel.ChannelHandlerContext; | ||
| import io.netty.channel.SimpleChannelInboundHandler; | ||
| import org.slf4j.Logger; | ||
| import org.slf4j.LoggerFactory; | ||
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| import org.apache.spark.network.buffer.ManagedBuffer; | ||
| import org.apache.spark.network.client.TransportClient; | ||
| import org.apache.spark.network.protocol.ChunkFetchFailure; | ||
| import org.apache.spark.network.protocol.ChunkFetchRequest; | ||
| import org.apache.spark.network.protocol.ChunkFetchSuccess; | ||
| import org.apache.spark.network.protocol.Encodable; | ||
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| import static org.apache.spark.network.util.NettyUtils.*; | ||
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| /** | ||
| * A dedicated ChannelHandler for processing ChunkFetchRequest messages. When sending response | ||
| * of ChunkFetchRequest messages to the clients, the thread performing the I/O on the underlying | ||
| * channel could potentially be blocked due to disk contentions. If several hundreds of clients | ||
| * send ChunkFetchRequest to the server at the same time, it could potentially occupying all | ||
| * threads from TransportServer's default EventLoopGroup for waiting for disk reads before it | ||
| * can send the block data back to the client as part of the ChunkFetchSuccess messages. As a | ||
| * result, it would leave no threads left to process other RPC messages, which takes much less | ||
| * time to process, and could lead to client timing out on either performing SASL authentication, | ||
| * registering executors, or waiting for response for an OpenBlocks messages. | ||
| */ | ||
| public class ChunkFetchRequestHandler extends SimpleChannelInboundHandler<ChunkFetchRequest> { | ||
| private static final Logger logger = LoggerFactory.getLogger(ChunkFetchRequestHandler.class); | ||
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| private final TransportClient client; | ||
| private final StreamManager streamManager; | ||
| /** The max number of chunks being transferred and not finished yet. */ | ||
| private final long maxChunksBeingTransferred; | ||
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| public ChunkFetchRequestHandler( | ||
| TransportClient client, | ||
| StreamManager streamManager, | ||
| Long maxChunksBeingTransferred) { | ||
| this.client = client; | ||
| this.streamManager = streamManager; | ||
| this.maxChunksBeingTransferred = maxChunksBeingTransferred; | ||
| } | ||
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| @Override | ||
| public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { | ||
| logger.warn("Exception in connection from " + getRemoteAddress(ctx.channel()), | ||
| cause); | ||
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Contributor
There was a problem hiding this comment. spacing 2, fix throughout the file
Contributor
There was a problem hiding this comment. this can actually be unwrapped here |
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| ctx.close(); | ||
| } | ||
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| @Override | ||
| protected void channelRead0(ChannelHandlerContext ctx, | ||
| final ChunkFetchRequest msg) throws Exception { | ||
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| Channel channel = ctx.channel(); | ||
| if (logger.isTraceEnabled()) { | ||
| logger.trace("Received req from {} to fetch block {}", getRemoteAddress(channel), | ||
| msg.streamChunkId); | ||
| } | ||
| long chunksBeingTransferred = streamManager.chunksBeingTransferred(); | ||
| if (chunksBeingTransferred >= maxChunksBeingTransferred) { | ||
| logger.warn("The number of chunks being transferred {} is above {}, close the connection.", | ||
| chunksBeingTransferred, maxChunksBeingTransferred); | ||
| channel.close(); | ||
| return; | ||
| } | ||
| ManagedBuffer buf; | ||
| try { | ||
| streamManager.checkAuthorization(client, msg.streamChunkId.streamId); | ||
| streamManager.registerChannel(channel, msg.streamChunkId.streamId); | ||
| buf = streamManager.getChunk(msg.streamChunkId.streamId, msg.streamChunkId.chunkIndex); | ||
| } catch (Exception e) { | ||
| logger.error(String.format("Error opening block %s for request from %s", | ||
| msg.streamChunkId, getRemoteAddress(channel)), e); | ||
| respond(channel, | ||
| new ChunkFetchFailure(msg.streamChunkId, | ||
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Contributor
There was a problem hiding this comment. fix wrapping and sapcing |
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| Throwables.getStackTraceAsString(e))); | ||
| return; | ||
| } | ||
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| streamManager.chunkBeingSent(msg.streamChunkId.streamId); | ||
| respond(channel, new ChunkFetchSuccess(msg.streamChunkId, buf)).addListener( | ||
| (ChannelFutureListener) future -> streamManager.chunkSent(msg.streamChunkId.streamId)); | ||
| } | ||
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| /** | ||
| * The invocation to channel.writeAndFlush is async, and the actual I/O on the | ||
| * channel will be handled by the EventLoop the channel is registered to. So even | ||
| * though we are processing the ChunkFetchRequest in a separate thread pool, the actual I/O, | ||
| * which is the potentially blocking call that could deplete server handler threads, is still | ||
| * being processed by TransportServer's default EventLoopGroup. In order to throttle the max | ||
| * number of threads that channel I/O for sending response to ChunkFetchRequest, the thread | ||
| * calling channel.writeAndFlush will wait for the completion of sending response back to | ||
| * client by invoking sync(). This will throttle the rate at which threads from | ||
| * ChunkFetchRequest dedicated EventLoopGroup submit channel I/O requests to TransportServer's | ||
| * default EventLoopGroup, thus making sure that we can reserve some threads in | ||
| * TransportServer's default EventLoopGroup for handling other RPC messages. | ||
| */ | ||
| private ChannelFuture respond(final Channel channel, | ||
| final Encodable result) throws InterruptedException { | ||
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| final SocketAddress remoteAddress = channel.remoteAddress(); | ||
| return channel.writeAndFlush(result).sync().addListener((ChannelFutureListener) future -> { | ||
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Contributor
There was a problem hiding this comment. do we actually want to use await() here instead of sync(). Sync says "Waits for this future until it is done, and rethrows the cause of the failure if this future failed." I'm not sure we want a rethrow here since we have the addListener to handle the future failure.
Author
There was a problem hiding this comment. Yes await can be used as well... i will test it out and let you know its ramifications if any, thanks
Author
There was a problem hiding this comment. ok i figured the following... i think it better to rethrow a.k.a. use sync() instead of quitely logging the exception via await(). The reason being as follows.... The respond call made here https://github.com/apache/spark/pull/22173/files#diff-a37b07d454be4d6cd26edb294661d4e3R106 waits for sending the failed or success response back. Hence, it is a blocking call. If an exception is thrown using await() we log quitely and do no rethrow, the underlying rpc handler will not know about the request status here https://github.com/apache/spark/blob/master/common/network-common/src/main/java/org/apache/spark/network/server/TransportRequestHandler.java#L183, rethrowing the exception allows it to handle and throw an rpc failure here https://github.com/apache/spark/blob/master/common/network-common/src/main/java/org/apache/spark/network/server/TransportRequestHandler.java#L194 else we have to wait for a timeout exception instead of an Interrupt exception. Either cases this seems fine but using sync() we will fail fast...
Contributor
There was a problem hiding this comment. so it doesn't go through https://github.com/apache/spark/blob/master/common/network-common/src/main/java/org/apache/spark/network/server/TransportRequestHandler.java#L183 since that is hte rpchandler . The TransportChannelHandler won't handle it at all, it will go to the pipeline which calls the ChunkFetchRequestHandler. So whatever is calling that is what would get the exception propogated. The reason I said this is because previously when this was handled in TransportChannelHandler, it wasn't throwing the exception up. The TrasnportRequestHandler.respond is calling hte writeAndFlush async and then just adding a listener which would simply log an error if the future wasn't successful.
Author
There was a problem hiding this comment. ok i had chunkFetchHandler as an instance of rpcHandler in my mind...
Author
There was a problem hiding this comment. It justs logs the exception but the behaviour is same… as in the first case an additional warning from netty side is passed onto the listener and the channel is closed… in the later we quitely log error and the channel is closed… the executors deal with the closed channel and retry or schedule the task on different executor… and eventually the job seems to succeed… in the example i ran… i expect the retry to go through in such scenarios… i will just use await() as the ERROR is logged and we dont have to be more verbose with the warning from the netty side... |
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| if (future.isSuccess()) { | ||
| logger.trace("Sent result {} to client {}", result, remoteAddress); | ||
| } else { | ||
| logger.error(String.format("Error sending result %s to %s; closing connection", | ||
| result, remoteAddress), future.cause()); | ||
| channel.close(); | ||
| } | ||
| }); | ||
| } | ||
| } | ||
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Is there any special reason that this must be a global one? I have not yet looked the details. But looks like this may cause ChunkFetchIntegrationSuite flaky as there is no isolation between tests.
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I haven't been able to reproduce this but the number of threads used for this tests are 2* number of cores or spark.shuffle.io.serverThreads.