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https://issues.apache.org/jira/browse/HDFS-11922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16161409#comment-16161409
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Anu Engineer commented on HDFS-11922:
-------------------------------------
[~cheersyang] & [~yuanbo] Thanks for designing and getting this work done. It
is amazing and takes us very close to the ozone trunk merge. Really appreciate
all your hard work. Thanks to all the reviewers too, really appreciate all of
you pitching in to complete this work.
> Ozone: KSM: Garbage collect deleted blocks
> ------------------------------------------
>
> Key: HDFS-11922
> URL: https://issues.apache.org/jira/browse/HDFS-11922
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ozone
> Reporter: Anu Engineer
> Assignee: Weiwei Yang
> Priority: Critical
> Fix For: HDFS-7240
>
> Attachments: Asynchronous key delete .pdf
>
>
> We need to garbage collect deleted blocks from the Datanodes. There are two
> cases where we will have orphaned blocks. One is like the classical HDFS,
> where someone deletes a key and we need to delete the corresponding blocks.
> Another case, is when someone overwrites a key -- an overwrite can be treated
> as a delete and a new put -- that means that older blocks need to be GC-ed at
> some point of time.
> Couple of JIRAs has discussed this in one form or another -- so consolidating
> all those discussions in this JIRA.
> HDFS-11796 -- needs to fix this issue for some tests to pass
> HDFS-11780 -- changed the old overwriting behavior to not supporting this
> feature for time being.
> HDFS-11920 - Once again runs into this issue when user tries to put an
> existing key.
> HDFS-11781 - delete key API in KSM only deletes the metadata -- and relies on
> GC for Datanodes.
> When we solve this issue, we should also consider 2 more aspects.
> One, we support versioning in the buckets, tracking which blocks are really
> orphaned is something that KSM will do. So delete and overwrite at some point
> needs to decide how to handle versioning of buckets.
> Two, If a key exists in a closed container, then it is immutable, hence the
> strategy of removing the key might be more complex than just talking to an
> open container.
> cc : [~xyao], [~cheersyang], [~vagarychen], [~msingh], [~yuanbo],
> [~szetszwo], [~nandakumar131]
>
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