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https://issues.apache.org/jira/browse/HDFS-8881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14680944#comment-14680944
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Jing Zhao commented on HDFS-8881:
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Thanks for the fix, Walter! The patch looks good to me overall. Some comments:
# We can put the following conditions into a single function
{code}
+ if (numCurrentReplica > fileReplication
+ || (storedBlock.isStriped() && numCurrentReplica == fileReplication
+ && hasOverReplicatedLiveInternalBlock(storedBlock))) {
{code}
# For {{hasOverReplicatedLiveInternalBlock}}, maybe we only need to check
{{BlockInfoStriped#triplets}} or {{indices}}. Currently all the redundant
internal replicas start from index 9 in triplets/indices. Maybe we can define a
function inside of {{BlockInfoStriped}}, which utilizes this logic to check if
any internal block has redundant replicas. Then
{{hasOverReplicatedLiveInternalBlock}} can call this function to check.
> Erasure Coding: internal blocks got missed and got over-replicated at the
> same time
> -----------------------------------------------------------------------------------
>
> Key: HDFS-8881
> URL: https://issues.apache.org/jira/browse/HDFS-8881
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Walter Su
> Assignee: Walter Su
> Attachments: HDFS-8881.00.patch
>
>
> We know the Repl checking depends on {{BlockManager#countNodes()}}, but
> countNodes() has limitation for striped blockGroup.
> *One* missing internal block will be catched by Repl checking, and handled by
> ReplicationMonitor.
> *One* over-replicated internal block will be catched by Repl checking, and
> handled by processOverReplicatedBlocks.
> *One* missing internal block and *two* over-replicated internal blocks *at
> the same time* will be catched by Repl checking, and handled by
> processOverReplicatedBlocks, later by ReplicationMonitor.
> *One* missing internal block and *One* over-replicated internal block *at the
> same time* will *NOT* be catched by Repl checking.
> "at the same time" means one missing internal block can't be recovered, and
> one internal block got over-replicated anyway. For example:
> scenario A:
> step 1. block #0 and #1 are reported missing.
> 2. a new #1 got recovered.
> 3. the old #1 come back, and the recovery work for #0 failed.
> scenario B:
> 1. An DN decommissioned/dead which has #1.
> 2. block #0 is reported missing.
> 3. The DN has #1 recommisioned, and the recovery work for #0 failed.
> In the end, the blockGroup has \[1, 1, 2, 3, 4, 5, 6, 7, 8\], assume 6+3
> schema. Client always needs to decode #0 if the blockGroup doesn't get
> handled.
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