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From "Dmytro Molkov (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-1245) Plugable block id generation
Date Fri, 18 Jun 2010 00:00:25 GMT
Plugable block id generation 

                 Key: HDFS-1245
                 URL: https://issues.apache.org/jira/browse/HDFS-1245
             Project: Hadoop HDFS
          Issue Type: New Feature
          Components: name-node
            Reporter: Dmytro Molkov

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:

void blockAdded(Block)
void blockRemoved(Block)
Block nextBlock()

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?

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