[jira] [Resolved] (HDFS-16659) JournalNode should throw NewerTxnIdException if SinceTxId is bigger than HighestWrittenTxId

["Erik Krogen (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-16659?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Erik Krogen resolved HDFS-16659.
--------------------------------
    Fix Version/s: 3.4.0
       Resolution: Fixed

> JournalNode should throw NewerTxnIdException if SinceTxId is bigger than HighestWrittenTxId
> -------------------------------------------------------------------------------------------
>
>                 Key: HDFS-16659
>                 URL: https://issues.apache.org/jira/browse/HDFS-16659
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: ZanderXu
>            Assignee: ZanderXu
>            Priority: Critical
>              Labels: pull-request-available
>             Fix For: 3.4.0
>
>          Time Spent: 1h
>  Remaining Estimate: 0h
>
> JournalNode should throw `CacheMissException` if `sinceTxId` is bigger than `highestWrittenTxId` during handling `getJournaledEdits` rpc from NNs. 
> Current logic may cause in-progress EditlogTailer cannot replay any Edits from JournalNodes in some corner cases, resulting in ObserverNameNode cannot handle requests from clients.
> Suppose there are 3 journalNodes, JN0 ~ JN1.
> * JN0 has some abnormal cases when Active Namenode is syncing 10 Edits with first txid 11
> * NameNode just ignore the abnormal JN0 and continue to sync Edits to Journal 1 and 2
> * JN0 backed to health
> * NameNode continue sync 10 Edits with first txid 21.
> * At this point, there are no Edits 11 ~ 30 in the cache of JN0
> * Observer NameNode try to select EditLogInputStream through `getJournaledEdits` with since txId 21
> * Journal 2 has some abnormal cases and caused a slow response
> The expected result is: Response should contain 20 Edits from txId 21 to txId 30 from JN1 and JN2. Because Active NameNode successfully write these Edits to JN1 and JN2 and failed write these edits to JN0.
> But in the current implementation,  the response is [Response(0) from JN0, Response(10) from JN1], because  there are some abnormal cases in  JN2, such as GC, bad network,  cause a slow response. So the `maxAllowedTxns` will be 0, NameNode will not replay any Edits.
> As above, the root case is that JournalNode should throw Miss Cache Exception when `sinceTxid` is more than `highestWrittenTxId`.
> And the bug code as blew:
> {code:java}
> if (sinceTxId > getHighestWrittenTxId()) {
>     // Requested edits that don't exist yet; short-circuit the cache here
>     metrics.rpcEmptyResponses.incr();
>     return GetJournaledEditsResponseProto.newBuilder().setTxnCount(0).build(); 
> }
> {code}



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