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From "Kan Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6889) Make RPC to have an option to timeout
Date Tue, 10 Aug 2010 01:11:18 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6889?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12896754#action_12896754
] 

Kan Zhang commented on HADOOP-6889:
-----------------------------------

If we can confirm Java always uses the same object for the same integer, your code is correct.
Otherwise, I'm fine with using rpcTimeout as hashcode. I've seen recommendations on computing
hashcode iteratively as follows.
{code}
hash = PRIME * hash + component_value
{code}
Seems we are doing ^ instead of +. Does it matter?

> Make RPC to have an option to timeout
> -------------------------------------
>
>                 Key: HADOOP-6889
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6889
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: ipc
>    Affects Versions: 0.22.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0, 0.20-append
>
>         Attachments: ipcTimeout.patch, ipcTimeout1.patch, ipcTimeout2.patch
>
>
> Currently Hadoop RPC does not timeout when the RPC server is alive. What it currently
does is that a RPC client sends a ping to the server whenever a socket timeout happens. If
the server is still alive, it continues to wait instead of throwing a SocketTimeoutException.
This is to avoid a client to retry when a server is busy and thus making the server even busier.
This works great if the RPC server is NameNode.
> But Hadoop RPC is also used for some of client to DataNode communications, for example,
for getting a replica's length. When a client comes across a problematic DataNode, it gets
stuck and can not switch to a different DataNode. In this case, it would be better that the
client receives a timeout exception.
> I plan to add a new configuration ipc.client.max.pings that specifies the max number
of pings that a client could try. If a response can not be received after the specified max
number of pings, a SocketTimeoutException is thrown. If this configuration property is not
set, a client maintains the current semantics, waiting forever.

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