The idea is to have a way to easily create block id generation engines that may fit a certain purpose. One of them could be
HDFS-898 started by Konstantin, but potentially others.
We chatted with Dhruba about this for a while and came up with the following approach:
There should be a BlockIDGenerator interface that has following methods:
First two methods are needed for block generation engines that hold a certain state. During the restart, when namenode reads the fsimage it will notify generator about all the blocks it reads from the image and during runtime namenode will notify the generator about block removals on file deletion.
The instance of the generator will also have a reference to the block registry, the interface that BlockManager implements. The only method there is _blockExists(Block)_, so that the current random block id generation can be implemented, since it needs to check with the block manager if the id is already present.
What does the community think about this proposal?