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https://issues.apache.org/jira/browse/HDFS-9381?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uma Maheswara Rao G updated HDFS-9381:
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Attachment: HDFS-9381.01.patch
Thanks Rakesh for taking a look.
I have slightly modified version of the patch here. It followed other
approach, that is introduced a new list called
"unscheduledPendingReplications", while processing in Replication monitor and
if we want to add a block to pending replications with out scheduling, then we
can use this list. This items could be processed in 2 cases.
1. When block reported from DN to NN and already scheduled replication success.
Block got removed from pending replications(via pendingReplications@decrement)
2. Previously scheduled replication was not success and block timeout in
pendingReplications. That time block will be moved to toNeededReplications
back, so this block element will be cleared from unscheduledPendingReplications
list now.
Please take a look if this works out to handle this case.
> When same block came for replication for Striped mode, we can move that block
> to PendingReplications
> ----------------------------------------------------------------------------------------------------
>
> Key: HDFS-9381
> URL: https://issues.apache.org/jira/browse/HDFS-9381
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: erasure-coding, namenode
> Affects Versions: 3.0.0
> Reporter: Uma Maheswara Rao G
> Assignee: Uma Maheswara Rao G
> Attachments: HDFS-9381.00.patch, HDFS-9381.01.patch
>
>
> Currently I noticed that we are just returning null if block already exists
> in pendingReplications in replication flow for striped blocks.
> {code}
> if (block.isStriped()) {
> if (pendingNum > 0) {
> // Wait the previous recovery to finish.
> return null;
> }
> {code}
> Here if we just return null and if neededReplications contains only fewer
> blocks(basically by default if less than numliveNodes*2), then same blocks
> can be picked again from neededReplications from next loop as we are not
> removing element from neededReplications. Since this replication process need
> to take fsnamesystmem lock and do, we may spend some time unnecessarily in
> every loop.
> So my suggestion/improvement is:
> Instead of just returning null, how about incrementing pendingReplications
> for this block and remove from neededReplications? and also another point to
> consider here is, to add into pendingReplications, generally we need target
> and it is nothing but to which node we issued replication command. Later when
> after replication success and DN reported it, block will be removed from
> pendingReplications from NN addBlock.
> So since this is newly picked block from neededReplications, we would not
> have selected target yet. So which target to be passed to pendingReplications
> if we add this block? One Option I am thinking is, how about just passing
> srcNode itself as target for this special condition? So, anyway if the block
> is really missed, srcNode will not report it. So this block will not be
> removed from pending replications, so that when it is timed out, it will be
> considered for replication again and that time it will find actual target to
> replicate while processing as part of regular replication flow.
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