1. This bug contributed to the crash discussed in
HADOOP-572.
The problem is that when the name-node is busy, and is not able to process all requests from its clients,
it can consider one of data-nodes dead and discard its blocks sending them into the neededRelications list.
When it finally gets the heartbeat from this data-node it resurrects the node, but not the data-node blocks,
and hence continues to replicate them.
Of course, eventually the name-node will receive the block report from this data-node, but it could take up
to 1 hour. During this time it proceeds with unnecessary block replications, which could be avoided if the
data-node sent its block report right after the resurrection.
I modified code so that the name-node requests block report if it receives a heartbeat from a dead data-node.
I introduced a new command type in the BlockCommand class.
I replaced multiple boolean indicators of the command types by one enum field.
I changed the DatanodeProtocol version.
2. This patch also includes a fix for the data-node registration. If a data-nodes times out during registration
it silently exits, which is hard to notice with a large number of nodes. This patch places registration in a loop,
so that it could retry.
Bug
Closed
Major
Name-node should demand a block report from resurrected data-nodes.
