Without the patch in
HDFS-1108, new block allocations aren't logged to the edits log. For HA, we'll need that functionality and we'll need to make sure that block locations aren't blown away in the Standby NN when tailing the edits log.
As described in
When we close a file, or add another block to a file, we write OP_CLOSE or OP_ADD in the txn log. FSEditLogLoader, when it sees these types of transactions, creates new BlockInfo objects for all of the blocks listed in the transaction. These new BlockInfos have no block locations associated. So, when we close a file, the SBNN loses its block locations info for that file and is no longer "hot".
I have an ugly hack which copies over the old BlockInfos from the existing INode, but I'm not convinced it's the right way. It might be cleaner to add new opcode types like OP_ADD_ADDITIONAL_BLOCK, and actually treat OP_CLOSE as just a finalization of INodeFileUnderConstruction to INodeFile, rather than replacing block info at all.