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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1245) Plugable block id generation
Date Sat, 12 Jan 2013 01:59:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1245?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13551757#comment-13551757

Konstantin Shvachko commented on HDFS-1245:

I would like to resurrect this jira.
Now that we have {{GenerationStamp}} and {{INodeId}} generators, it would be logical to wrap
block id generation into a class.
I plan to introduce BlockIdGenerator, which generates random ids.
Making it pluggable will depend on whether anybody wants to build another generator.
It may make sense to implement Dhruba's suggestion in HDFS-898 to let people use random generator
on old clusters, and format new ones with the sequential block id generator. Old clusters
can also go through the procedure I described in HDFS-898, which can be achieved by one-time
image processing to find the biggest hole between existing random block ids, and then switch
to sequential generation within that hole.
> 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
>            Reporter: Dmytro Molkov
>            Assignee: 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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