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https://issues.apache.org/jira/browse/HDFS-1245?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13552116#comment-13552116
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Konstantin Shvachko commented on HDFS-1245:
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This makes the block id generation pluggable. One can override
{{FSImage.createBlockIdGenerator()}} to define a new generator. May be not
exactly as it was originally planned, but pluggable.
> Plugable block id generation
> -----------------------------
>
> Key: HDFS-1245
> URL: https://issues.apache.org/jira/browse/HDFS-1245
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: namenode
> Affects Versions: 0.22.0
> Reporter: Dmytro Molkov
> Assignee: Konstantin Shvachko
> Attachments: blockIdGenerator-branch2.patch, blockIdGenerator.patch
>
>
> 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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