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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7590) Add a costless notifications mechanism from master to regionservers & clients
Date Wed, 27 Feb 2013 18:03:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13588563#comment-13588563
] 

Hadoop QA commented on HBASE-7590:
----------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12571229/7590.v2.patch
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:green}+1 tests included{color}.  The patch appears to include 17 new or modified
tests.

    {color:green}+1 hadoop2.0{color}.  The patch compiles against the hadoop 2.0 profile.

    {color:green}+1 javadoc{color}.  The javadoc tool did not generate any warning messages.

    {color:red}-1 javac{color}.  The patch appears to cause mvn compile goal to fail.

    {color:red}-1 findbugs{color}.  The patch appears to cause Findbugs (version 1.3.9) to
fail.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:green}+1 lineLengths{color}.  The patch does not introduce lines longer than 100

     {color:red}-1 core tests{color}.  The patch failed these unit tests:
     

Test results: https://builds.apache.org/job/PreCommit-HBASE-Build/4580//testReport/
Console output: https://builds.apache.org/job/PreCommit-HBASE-Build/4580//console

This message is automatically generated.
                
> Add a costless notifications mechanism from master to regionservers & clients
> -----------------------------------------------------------------------------
>
>                 Key: HBASE-7590
>                 URL: https://issues.apache.org/jira/browse/HBASE-7590
>             Project: HBase
>          Issue Type: Bug
>          Components: Client, master, regionserver
>    Affects Versions: 0.96.0
>            Reporter: nkeywal
>            Assignee: nkeywal
>         Attachments: 7590.inprogress.patch, 7590.v1.patch, 7590.v1-rebased.patch, 7590.v2.patch
>
>
> t would be very useful to add a mechanism to distribute some information to the clients
and regionservers. Especially It would be useful to know globally (regionservers + clients
apps) that some regionservers are dead. This would allow:
> - to lower the load on the system, without clients using staled information and going
on dead machines
> - to make the recovery faster from a client point of view. It's common to use large timeouts
on the client side, so the client may need a lot of time before declaring a region server
dead and trying another one. If the client receives the information separatly about a region
server states, it can take the right decision, and continue/stop to wait accordingly.
> We can also send more information, for example instructions like 'slow down' to instruct
the client to increase the retries delay and so on.
>  Technically, the master could send this information. To lower the load on the system,
we should:
> - have a multicast communication (i.e. the master does not have to connect to all servers
by tcp), with once packet every 10 seconds or so.
> - receivers should not depend on this: if the information is available great. If not,
it should not break anything.
> - it should be optional.
> So at the end we would have a thread in the master sending a protobuf message about the
dead servers on a multicast socket. If the socket is not configured, it does not do anything.
On the client side, when we receive an information that a node is dead, we refresh the cache
about it.

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