Major Description
Currently the postBulkLoadHFile() hook notifies the locations of bulk loaded hfiles.
However, if bulk load fails after hfile is moved to region directory but before postBulkLoadHFile() hook is called, there is no way for pluggable components (replication - see HBASE-17290, backup / restore) to know which hfile(s) have been moved to region directory.
Even if postBulkLoadHFile() is called in finally block, the write (to backup table or zookeeper) issued from postBulkLoadHFile() may fail, ending up with same situation.
This issue adds a preCommitStoreFile() hook which notifies path of to be committed hfile before bulk loaded hfile is moved to region directory.
With preCommitStoreFile() hook, write (to backup table or zookeeper) can be issued before the movement of hfile.
If write fails, IOException would make bulk load fail, not leaving hfile in region directory.