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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2312) Possible data loss when RS goes into GC pause while rolling HLog
Date Mon, 09 Aug 2010 19:52:43 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12896680#action_12896680
] 

stack commented on HBASE-2312:
------------------------------

When I apply this patch to trunk, unit tests hang.  Are we missing something from our hadoop
Nicolas?  We have 0.20.3-append-r964955-1240 committed to trunk (Thats the svn revision and
patch 1240 applied).

I see for example that the TestZookeeper is stuck doing this:

{code}

2010-08-09 12:45:23,964 WARN  [IPC Server handler 6 on 62023] namenode.FSNamesystem(1166):
DIR* NameSystem.startFile: failed to create file /user/Stack/.logs/h135.sfo.stumble.net,62051,1281382952055-splitting/10.10.1.135%3A62051.1281382952241
for DFSClient_-1591590456 on client 127.0.0.1, because this file is already being created
by DFSClient_hb_m_10.10.1.135:62037 on 127.0.0.1
2010-08-09 12:45:23,965 WARN  [master] util.FSUtils(631): Waited 151520ms for lease recovery
on hdfs://localhost:62023/user/Stack/.logs/h135.sfo.stumble.net,62051,1281382952055-splitting/10.10.1.135%3A62051.1281382952241:org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException:
failed to create file /user/Stack/.logs/h135.sfo.stumble.net,62051,1281382952055-splitting/10.10.1.135%3A62051.1281382952241
for DFSClient_-1591590456 on client 127.0.0.1, because this file is already being created
by DFSClient_hb_m_10.10.1.135:62037 on 127.0.0.1
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFileInternal(FSNamesystem.java:1093)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.appendFile(FSNamesystem.java:1181)
        at org.apache.hadoop.hdfs.server.namenode.NameNode.append(NameNode.java:396)
        at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:961)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:957)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:955)
{code}

This test passes if I do not have /HBASE-2312-2.patch  in place.

> Possible data loss when RS goes into GC pause while rolling HLog
> ----------------------------------------------------------------
>
>                 Key: HBASE-2312
>                 URL: https://issues.apache.org/jira/browse/HBASE-2312
>             Project: HBase
>          Issue Type: Bug
>          Components: master, regionserver
>    Affects Versions: 0.20.3
>            Reporter: Karthik Ranganathan
>            Assignee: Nicolas Spiegelberg
>             Fix For: 0.90.0
>
>
> There is a very corner case when bad things could happen(ie data loss):
> 1)	RS #1 is going to roll its HLog - not yet created the new one, old one will get no
more writes
> 2)	RS #1 enters GC Pause of Death
> 3)	Master lists HLog files of RS#1 that is has to split as RS#1 is dead, starts splitting
> 4)	RS #1 wakes up, created the new HLog (previous one was rolled) and appends an edit
- which is lost
> The following seems like a possible solution:
> 1)	Master detects RS#1 is dead
> 2)	The master renames the /hbase/.logs/<regionserver name>  directory to something
else (say /hbase/.logs/<regionserver name>-dead)
> 3)	Add mkdir support (as opposed to mkdirs) to HDFS - so that a file create fails if
the directory doesn't exist. Dhruba tells me this is very doable.
> 4)	RS#1 comes back up and is not able create the new hlog. It restarts itself.

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