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https://issues.apache.org/jira/browse/HADOOP-13436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15399409#comment-15399409
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Daryn Sharp commented on HADOOP-13436:
--------------------------------------
bq. Does it mean it leads to performance issues?
Technically yes, but if the total code path was profiled it's probably not even
a blip. I took a look at {{MultipleLinearRandomRetry}} and actually caches the
{{toString()}} value so it's not an issue with that policy.
Now the problem is making sure all current and future policies properly adhere
to a contract required to ensure connection lookups work correctly. I'd
suggest that {{RetryPolicy}} should be an abstract class rather than an
interface. This will ensure the contract is enforced.
{{RetryPolicy}} would implement {{hashCode}}, {{equals}}, and {{toString}} as
final methods using the impl of {{MultipleLinearRandomRetry}}. Except
{{toString}} would call a new abstract {{getName}} as the value it will cache.
If compatibility is an overriding concern then I guess a new abstract class,
ex. {{AbstractRetryPolicy}}, that implements {{RetryPolicy}} could be created.
Existing polices would then extend that class. This has the downside of future
policies re-introducing this jira's buggy behavior.
> RPC connections are leaking due to missing equals override in
> RetryUtils#getDefaultRetryPolicy
> ----------------------------------------------------------------------------------------------
>
> Key: HADOOP-13436
> URL: https://issues.apache.org/jira/browse/HADOOP-13436
> Project: Hadoop Common
> Issue Type: Bug
> Components: ipc
> Affects Versions: 2.7.1
> Reporter: Xiaobing Zhou
> Assignee: Xiaobing Zhou
> Attachments: repro.sh
>
>
> We've noticed RPC connections are increasing dramatically in a Kerberized
> HDFS cluster with {noformat}dfs.client.retry.policy.enabled{noformat}
> enabled. Internally, Client#getConnection is doing lookup relying on
> ConnectionId#equals, which composes checking Subclass-of-RetryPolicy#equals.
> If subclasses of RetryPolicy neglect overriding RetryPolicy#equals, every
> instances 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#equals.
> This is stack trace where RetryUtils#getDefaultRetryPolicy is called:
> {noformat}
> 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)
> {noformat}
> 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.
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