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Chao Sun commented on HDFS-13924: --------------------------------- [~xkrogen] brought up a good point in [HDFS-13898|https://issues.apache.org/jira/browse/HDFS-13898?focusedCommentId=16622255&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16622255]: if we throw exception from the server side, it may lead to frequent re-scanning of observers from the ORPP side. Instead we can throw a special exception and make ORPP to directly retry active in this case. > Handle BlockMissingException when reading from observer > ------------------------------------------------------- > > Key: HDFS-13924 > URL: https://issues.apache.org/jira/browse/HDFS-13924 > Project: Hadoop HDFS > Issue Type: Sub-task > Reporter: Chao Sun > Priority: Major > > Internally we found that reading from ObserverNode may result to > {{BlockMissingException}}. This may happen when the observer sees a smaller > number of DNs than active (maybe due to communication issue with those DNs), > or (we guess) late block reports from some DNs to the observer. This error > happens in > [DFSInputStream#chooseDataNode|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java#L846], > when no valid DN can be found for the {{LocatedBlock}} got from the NN side. > One potential solution (although a little hacky) is to ask the > {{DFSInputStream}} to retry active when this happens. The retry logic already > present in the code - we just have to dynamically set a flag to ask the > {{ObserverReadProxyProvider}} try active in this case. > cc [~shv], [~xkrogen], [~vagarychen], [~zero45] for discussion. -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org