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https://issues.apache.org/jira/browse/HDFS-3908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486781#comment-13486781
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Uma Maheswara Rao G commented on HDFS-3908:
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I think this is general problem in HA than BKJM issue.
The problem what I am thinking is:
Active will continue even if there are some gaps in shared storage as that was
general editlog loading behaviour.
Also standby can not read the complete edits and may end up reading only till
the gapped edits as max and will not do any tailing further.
If this continues for long then standby will have big gap of edits and on
switch standby will fail to become active as it will not have continues edits.
@Xiao, is this the case you are seeing?
I think in HA case, we may have to expect shared storage edits mandatorily
instead of falling back on to local edits in case of edits missing in shared
storage while loading on startup. Because standby will have the input from only
shared storage to load edits.
In Non HA case, considering local edits from different namedirs should be fine.
But in HA, that should not be the case as explained above.
What about other's opinion on this proposal?
> 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 vm2/160.161.0.155
> ************************************************************/
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