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From "star (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-14314) fullBlockReportLeaseId should be reset after registering to NN
Date Tue, 26 Feb 2019 16:05:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-14314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16778122#comment-16778122
] 

star commented on HDFS-14314:
-----------------------------

[~hexiaoqiao], thanks. new patch updated.

> fullBlockReportLeaseId should be reset after registering to NN
> --------------------------------------------------------------
>
>                 Key: HDFS-14314
>                 URL: https://issues.apache.org/jira/browse/HDFS-14314
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 2.8.4
>         Environment:  
>  
>  
>            Reporter: star
>            Priority: Critical
>             Fix For: 2.8.4
>
>         Attachments: HDFS-14314-trunk.001.patch, HDFS-14314-trunk.001.patch, HDFS-14314-trunk.002.patch,
HDFS-14314.0.patch, HDFS-14314.2.patch, HDFS-14314.patch
>
>
>       since HDFS-7923 ,to rate-limit DN block report, DN will ask for a full block
lease id from active NN before sending full block to NN. Then DN will send full block report
together with lease id. If the lease id is invalid, NN will reject the full block report and
log "not in the pending set".
>       In a case when DN is doing full block reporting while NN is restarted. It
happens that DN will later send a full block report with lease id ,acquired from previous
NN instance, which is invalid to the new NN instance. Though DN recognized the new NN instance
by heartbeat and reregister itself, it did not reset the lease id from previous instance.
>       The issuse may cause DNs to temporarily go dead, making it unsafe to restart
NN especially in hadoop cluster which has large amount of DNs. HDFS-12914 reported the issue 
without any clues why it occurred and remain unsolved.
>        To make it clear, look at code below. We take it from method offerService
of class BPServiceActor. We eliminate some code to focus on current issue. fullBlockReportLeaseId
is a local variable to hold lease id from NN. Exceptions will occur at blockReport call when
NN restarting, which will be caught by catch block in while loop. Thus fullBlockReportLeaseId
will not be set to 0. After NN restarted, DN will send full block report which will be rejected
by the new NN instance. DN will never send full block report until the next full block report
schedule, about an hour later.
>       Solution is simple, just reset fullBlockReportLeaseId to 0 after any exception
or after registering to NN. Thus it will ask for a valid fullBlockReportLeaseId from new NN
instance.
> {code:java}
> private void offerService() throws Exception {
>   long fullBlockReportLeaseId = 0;
>   //
>   // Now loop for a long time....
>   //
>   while (shouldRun()) {
>     try {
>       final long startTime = scheduler.monotonicNow();
>       //
>       // Every so often, send heartbeat or block-report
>       //
>       final boolean sendHeartbeat = scheduler.isHeartbeatDue(startTime);
>       HeartbeatResponse resp = null;
>       if (sendHeartbeat) {
>       
>         boolean requestBlockReportLease = (fullBlockReportLeaseId == 0) &&
>                 scheduler.isBlockReportDue(startTime);
>         scheduler.scheduleNextHeartbeat();
>         if (!dn.areHeartbeatsDisabledForTests()) {
>           resp = sendHeartBeat(requestBlockReportLease);
>           assert resp != null;
>           if (resp.getFullBlockReportLeaseId() != 0) {
>             if (fullBlockReportLeaseId != 0) {
>               LOG.warn(nnAddr + " sent back a full block report lease " +
>                       "ID of 0x" +
>                       Long.toHexString(resp.getFullBlockReportLeaseId()) +
>                       ", but we already have a lease ID of 0x" +
>                       Long.toHexString(fullBlockReportLeaseId) + ". " +
>                       "Overwriting old lease ID.");
>             }
>             fullBlockReportLeaseId = resp.getFullBlockReportLeaseId();
>           }
>          
>         }
>       }
>    
>      
>       if ((fullBlockReportLeaseId != 0) || forceFullBr) {
>         //Exception occurred here when NN restarting
>         cmds = blockReport(fullBlockReportLeaseId);
>         fullBlockReportLeaseId = 0;
>       }
>       
>     } catch(RemoteException re) {
>       
>   } // while (shouldRun())
> } // offerService{code}
>  



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