Uma Maheswara Rao G created HDFS-9381:
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Summary: 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: namenode
Affects Versions: 3.0.0
Reporter: Uma Maheswara Rao G
Assignee: Uma Maheswara Rao G
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 neededReplications contains only fewer blocks(basically by default if
less than numliveNodes*2), then same blocks can be picked again from
neededReplications if we just return null 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 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 block is really
missed, srcNode anyway will not report it. So this block will not be removed
from pending replications, so that when it timeout, it will be considered for
replication and that time it will find actual target to replicate.
So
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