[HADOOP-13436] RPC connections are leaking due to not overriding hashCode and equals

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.7.1
• Component/s: ipc
• Assignee: Xiaobing Zhou
• Reporter: Xiaobing Zhou
• Created: 28/Jul/16 17:56
• Updated: 12/Jun/23 21:43

Description

We've noticed RPC connections are increasing dramatically in a Kerberized HDFS cluster with

dfs.client.retry.policy.enabled

enabled. Internally, Client#getConnection is doing lookup relying on ConnectionId #hashCode and then #equals, which compose checking Subclass-of-RetryPolicy #hashCode and #equals. If subclasses of RetryPolicy neglect overriding #hashCode or #equals, every instance of RetryPolicy with equivalent fields' values (e.g. MultipleLinearRandomRetry[6x10000ms, 10x60000ms]) will lead to a brand new connection because the check will fall back to Object#hashCode and Object#equals which is distinct and false for distinct instances.

This is stack trace where the anonymous RetryPolicy implementation (neglecting overriding hashCode and equals) in RetryUtils#getDefaultRetryPolicy is called:

at org.apache.hadoop.io.retry.RetryUtils.getDefaultRetryPolicy(RetryUtils.java:82)
        at org.apache.hadoop.hdfs.NameNodeProxies.createNNProxyWithClientProtocol(NameNodeProxies.java:409)
        at org.apache.hadoop.hdfs.NameNodeProxies.createNonHAProxy(NameNodeProxies.java:315)
        at org.apache.hadoop.hdfs.NameNodeProxies.createProxy(NameNodeProxies.java:176)
        at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:678)
        at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:619)
        at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:609)
        at org.apache.hadoop.hdfs.server.datanode.web.webhdfs.WebHdfsHandler.newDfsClient(WebHdfsHandler.java:272)
        at org.apache.hadoop.hdfs.server.datanode.web.webhdfs.WebHdfsHandler.onOpen(WebHdfsHandler.java:215)
        at org.apache.hadoop.hdfs.server.datanode.web.webhdfs.WebHdfsHandler.handle(WebHdfsHandler.java:135)
        at org.apache.hadoop.hdfs.server.datanode.web.webhdfs.WebHdfsHandler$1.run(WebHdfsHandler.java:117)
        at org.apache.hadoop.hdfs.server.datanode.web.webhdfs.WebHdfsHandler$1.run(WebHdfsHandler.java:114)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:422)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1657)
        at org.apache.hadoop.hdfs.server.datanode.web.webhdfs.WebHdfsHandler.channelRead0(WebHdfsHandler.java:114)
        at org.apache.hadoop.hdfs.server.datanode.web.URLDispatcher.channelRead0(URLDispatcher.java:52)
        at org.apache.hadoop.hdfs.server.datanode.web.URLDispatcher.channelRead0(URLDispatcher.java:32)
        at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
        at io.netty.channel.ChannelInboundHandlerAdapter.channelRead(ChannelInboundHandlerAdapter.java:86)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:163)
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:787)
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:130)
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:511)
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468)
        at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382)
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
        at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
        at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137)
        at java.lang.Thread.run(Thread.java:745)

Three options to fix the problem:
1. All subclasses of RetryPolicy must override equals and hashCode to deliver less discriminating equivalence relation, i.e. they are equal if they have meaningful equivalent fields' values (e.g. MultipleLinearRandomRetry[6x10000ms, 10x60000ms])
2. Change ConnectionId#equals by removing RetryPolicy#equals compoment.
3. Let WebHDFS reuse the DFSClient.

Issue Links

• relates to: HDFS-8855 Webhdfs client leaks active NameNode connections
• relates to: HDFS-7597 DelegationTokenIdentifier should cache the TokenIdentifier to UGI mapping

Sub-Tasks

• Have TryOnceThenFail implement ConnectionRetryPolicy: Patch Available
• Override equals and hashCode to avoid connection leakage: Resolved