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From "Han Xiao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3908) In HA mode, when there is a ledger in BK missing, which is generated after the last checkpoint, NN can not restore it.
Date Fri, 16 Nov 2012 01:41:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13498524#comment-13498524

Han Xiao commented on HDFS-3908:

You are right for the understanding. Two points:
1. If there is a gap in sharestorage, while a different gap in local, as the senario in the
Description. Should we let the NN start successfully? 
If we make it start, it is true the StandBy NN will not work normally. But we have a way to
recovery it: saveNameSpace of the Active NN, then copy to StandBy one. If we do nothing, either
NN will work, and there is no way to recovery, even in manaul.
2. If there is a gap in sharestorage, should we find a way to repair it if the gap exists
in local?
This will be a big revision. So we should consider 1st first, then 2st.
What do you think?
> In HA mode, when there is a ledger in BK missing, which is generated after the last checkpoint,
NN can not restore it.
> ----------------------------------------------------------------------------------------------------------------------
>                 Key: HDFS-3908
>                 URL: https://issues.apache.org/jira/browse/HDFS-3908
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>    Affects Versions: 2.0.1-alpha
>            Reporter: Han Xiao
> If not HA, when the num of edits.dir is larger than 1. Missing of one editlog file in
a dir will not relust problem cause of the replica in the other dir. 
> However, when in HA mode(using BK as ShareStorage), if an ledger missing, the missing
ledger will not restored at the phase of NN starting even if the related editlog file existing
in local dir.
> The missing maintains when NN is still in standby state. However, when the NN enters
active state, it will read the editlog file(related to the missing ledger) in local. But,
unfortunately, the ledger after the missing one in BK can't be readed at such a phase(cause
of gap).
> Therefore in the following situation, editlogs will not be restored even there is an
editlog file either in BK or in local dir: 
> In such a stituation, editlog can't be restored:
> 1、fsiamge file: fsimage_0000000000000005946.md5
> 2、legder in zk:
> 	\[zk: localhost:2181(CONNECTED) 0\] ls /hdfsEdit/ledgers/edits_00000000000000594
> 	edits_000000000000005941_000000000000005942
> 	edits_000000000000005943_000000000000005944
> 	edits_000000000000005945_000000000000005946
> 	edits_000000000000005949_000000000000005949   
> (missing edits_000000000000005947_000000000000005948)
> 3、editlog in local editlog dir:
> 	\-rw-r--r-- 1 root root      30 Sep  8 03:24 edits_0000000000000005947-0000000000000005948
> 	\-rw-r--r-- 1 root root 1048576 Sep  8 03:35 edits_0000000000000005950-0000000000000005950
> 	\-rw-r--r-- 1 root root 1048576 Sep  8 04:42 edits_0000000000000005951-0000000000000005951
> 	(miss edits_0000000000000005949-0000000000000005919)
> 4、and the seen_txid
> 	vm2:/tmp/hadoop-root/dfs/name/current # cat seen_txid
> 	5949
> Here, we want to restored editlog from txid 5946(image) to txid 5949(seen_txid). The
5947-5948 is missing in BK, 5949-5949 is missing in local dir.
> When start the NN, the following exception is thrown:
> 2012-09-08 06:26:10,031 FATAL org.apache.hadoop.hdfs.server.namenode.NameNode: Error
encountered requiring NN shutdown. Shutting down immediately.
> java.io.IOException: There appears to be a gap in the edit log.  We expected txid 5949,
but got txid 5950.
>         at org.apache.hadoop.hdfs.server.namenode.MetaRecoveryContext.editLogLoaderPrompt(MetaRecoveryContext.java:94)
>         at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadEditRecords(FSEditLogLoader.java:163)
>         at org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader.loadFSEdits(FSEditLogLoader.java:93)
>         at org.apache.hadoop.hdfs.server.namenode.FSImage.loadEdits(FSImage.java:692)
>         at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer.doTailEdits(EditLogTailer.java:223)
>         at org.apache.hadoop.hdfs.server.namenode.ha.EditLogTailer.catchupDuringFailover(EditLogTailer.java:182)
>         at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startActiveServices(FSNamesystem.java:599)
>         at org.apache.hadoop.hdfs.server.namenode.NameNode$NameNodeHAContext.startActiveServices(NameNode.java:1325)
>         at org.apache.hadoop.hdfs.server.namenode.ha.ActiveState.enterState(ActiveState.java:61)
>         at org.apache.hadoop.hdfs.server.namenode.ha.HAState.setStateInternal(HAState.java:63)
>         at org.apache.hadoop.hdfs.server.namenode.ha.StandbyState.setState(StandbyState.java:49)
>         at org.apache.hadoop.hdfs.server.namenode.NameNode.transitionToActive(NameNode.java:1233)
>         at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.transitionToActive(NameNodeRpcServer.java:990)
>         at org.apache.hadoop.ha.protocolPB.HAServiceProtocolServerSideTranslatorPB.transitionToActive(HAServiceProtocolServerSideTranslatorPB.java:107)
>         at org.apache.hadoop.ha.proto.HAServiceProtocolProtos$HAServiceProtocolService$2.callBlockingMethod(HAServiceProtocolProtos.java:3633)
>         at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:427)
>         at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:924)
>         at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1692)
>         at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1688)
>         at java.security.AccessController.doPrivileged(Native Method)
>         at javax.security.auth.Subject.doAs(Subject.java:396)
>         at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1232)
>         at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1686)
> 2012-09-08 06:26:10,036 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG:
> /************************************************************
> SHUTDOWN_MSG: Shutting down NameNode at vm2/
> ************************************************************/

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