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https://issues.apache.org/jira/browse/HDFS-17137?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiaoqiao He resolved HDFS-17137.
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Fix Version/s: 3.4.0
Hadoop Flags: Reviewed
Resolution: Fixed
> Standby/Observer NameNode skip to handle redundant replica block logic when
> set decrease replication.
> ------------------------------------------------------------------------------------------------------
>
> Key: HDFS-17137
> URL: https://issues.apache.org/jira/browse/HDFS-17137
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Haiyang Hu
> Assignee: Haiyang Hu
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.4.0
>
>
> Standby/Observer NameNode should not handle redundant replica block logic
> when set decrease replication.
> At present, when call setReplication to execute the logic of decrease
> replication,
> * ActiveNameNode will call the BlockManager#processExtraRedundancyBlock
> method to select the dn of the redundant replica , will add to the
> excessRedundancyMap and add to invalidateBlocks (RedundancyMonitor will be
> scheduled to delete the block on dn).
> * Then the StandyNameNode or ObserverNameNode load editlog and apply the
> SetReplicationOp, if the dn of the replica to be deleted has not yet
> performed incremental block report,
> here also will BlockManager#processExtraRedundancyBlock method be called here
> to select the dn of the redundant replica and add it to the
> excessRedundancyMap (here selected the redundant dn may be inconsistent with
> the dn selected in the active namenode).
> In excessRedundancyMap exist dn maybe affects the dn decommission, resulting
> can not to complete decommission dn operation in Standy/ObserverNameNode.
> The specific cases are as follows:
> For example a file is 3 replica (d1,d2,d3) and call setReplication set file
> to 2 replica.
> * ActiveNameNode select d1 with redundant replicas to add
> toexcessRedundancyMap and invalidateBlocks.
> * StandyNameNode replays SetReplicationOp (at this time, d1 has not yet
> executed incremental block report), so here maybe selected redundant replica
> dn are inconsistent with ActiveNameNode, such as select d2 to add
> excessRedundancyMap.
> * At this time, d1 completes deleting the block for incremental block report.
> * The DN list for this block in ActiveNameNode includes d2 and d3 (delete d1
> from in the excessRedundancyMap when processing the incremental block report
> ).
> * The DN list for this block in StandyNameNode includes d2 and d3 (can not
> delete d2 from in the excessRedundancyMap when processing the incremental
> block report).
> At this time, execute the decommission operation on d3.
> * ActiveNameNode will select a new node d4 to copy the replica, and d4 will
> run incrementally block report.
> * The DN list for this block in ActiveNameNode includes d2 and
> d3(decommissioning status),d4, then d3 can to decommissioned normally.
> * The DN list for this block in StandyNameNode is d3 (decommissioning
> status), d2 (redundant status), d4.
> since the requirements for two live replica are not met, d3 cannot be
> decommissioned at this time.
> Therefore, StandyNameNode or ObserverNameNode considers not process redundant
> replicas logic when call setReplication.
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