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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1263) retry logic when dfs exist or open fails temporarily, e.g because of timeout
Date Wed, 13 Jun 2007 06:26:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12504135
] 

Raghu Angadi commented on HADOOP-1263:
--------------------------------------

I am planning to use this framework for some new RPCs I am adding. I just want to confirm
if my understanding is correct: This patch adds a random exponential back off timeout starting
with 400 milliseconds for 5 times. In all 5 retries, this add a max of 12 seconds. Since client
RPC timeout is 60sec, time it takes for such RPC to fail takes between 300-312 seconds over
6 attempts. Is this expected?, because it is not exponential back off but essentially constant
timeout  of around 60sec for each retry.


> retry logic when dfs exist or open fails temporarily, e.g because of timeout
> ----------------------------------------------------------------------------
>
>                 Key: HADOOP-1263
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1263
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.12.3
>            Reporter: Christian Kunz
>            Assignee: Hairong Kuang
>             Fix For: 0.13.0
>
>         Attachments: retry.patch, retry1.patch
>
>
> Sometimes, when many (e.g. 1000+) map jobs start at about the same time and require supporting
files from filecache, it happens that some map tasks fail because of rpc timeouts. With only
the default number of 10 handlers on the namenode, the probability is high that the whole
job fails (see Hadoop-1182). It is much better with a higher number of handlers, but some
map tasks still fail.
> This could be avoided if rpc clients did retry when encountering a timeout before throwing
an exception.
> Examples of exceptions:
> java.net.SocketTimeoutException: timed out waiting for rpc response
> at org.apache.hadoop.ipc.Client.call(Client.java:473)
> at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:163)
> at org.apache.hadoop.dfs.$Proxy1.exists(Unknown Source)
> at org.apache.hadoop.dfs.DFSClient.exists(DFSClient.java:320)
> at org.apache.hadoop.dfs.DistributedFileSystem$RawDistributedFileSystem.exists(DistributedFileSystem.java:170)
> at org.apache.hadoop.dfs.DistributedFileSystem$RawDistributedFileSystem.open(DistributedFileSystem.java:125)
> at org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.(ChecksumFileSystem.java:110)
> at org.apache.hadoop.fs.ChecksumFileSystem.open(ChecksumFileSystem.java:330)
> at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:245)
> at org.apache.hadoop.filecache.DistributedCache.createMD5(DistributedCache.java:327)
> at org.apache.hadoop.filecache.DistributedCache.ifExistsAndFresh(DistributedCache.java:253)
> at org.apache.hadoop.filecache.DistributedCache.localizeCache(DistributedCache.java:169)
> at org.apache.hadoop.filecache.DistributedCache.getLocalCache(DistributedCache.java:86)
> at org.apache.hadoop.mapred.TaskRunner.run(TaskRunner.java:117)
> java.net.SocketTimeoutException: timed out waiting for rpc response
>         at org.apache.hadoop.ipc.Client.call(Client.java:473)
>         at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:163)
>         at org.apache.hadoop.dfs.$Proxy1.open(Unknown Source)
>         at org.apache.hadoop.dfs.DFSClient$DFSInputStream.openInfo(DFSClient.java:511)
>         at org.apache.hadoop.dfs.DFSClient$DFSInputStream.<init>(DFSClient.java:498)
>         at org.apache.hadoop.dfs.DFSClient.open(DFSClient.java:207)
>         at org.apache.hadoop.dfs.DistributedFileSystem$RawDistributedFileSystem.open(DistributedFileSystem.java:129)
>         at org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.<init>(ChecksumFileSystem.java:110)
>         at org.apache.hadoop.fs.ChecksumFileSystem.open(ChecksumFileSystem.java:330)
>         at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:245)
>         at org.apache.hadoop.fs.FileUtil.copy(FileUtil.java:82)
>         at org.apache.hadoop.fs.ChecksumFileSystem.copyToLocalFile(ChecksumFileSystem.java:577)
>         at org.apache.hadoop.fs.FileSystem.copyToLocalFile(FileSystem.java:766)
>         at org.apache.hadoop.mapred.TaskTracker.localizeJob(TaskTracker.java:370)
>         at org.apache.hadoop.mapred.TaskTracker.startNewTask(TaskTracker.java:877)
>         at org.apache.hadoop.mapred.TaskTracker.offerService(TaskTracker.java:545)
>         at org.apache.hadoop.mapred.TaskTracker.run(TaskTracker.java:913)
>         at org.apache.hadoop.mapred.TaskTracker.main(TaskTracker.java:1603)

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