...whether we need to let NameNode wait for all the block_received msgs to announce the replica is safe. Looking into the code, now we have
- NameNode knows the DataNodes involved when initially setting up the writing pipeline
- If any DataNode fails during the writing, client bumps the GS and finally reports all the DataNodes included in the new pipeline to NameNode through the updatePipeline RPC.
- When the client received the ack for the last packet of the block (and before the client tries to close the file on NameNode), the replica has been finalized in all the DataNodes.
Then in this case, when NameNode receives the close request from the client, the NameNode already knows the latest replicas for the block. Currently the checkReplication call only counts in all the replicas that NN has already received the block_received msg, but based on the above #2 and #3, it may be safe to also count in all the replicas in the BlockUnderConstructionFeature#replicas?