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https://issues.apache.org/jira/browse/HDFS-7430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14286495#comment-14286495
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Colin Patrick McCabe commented on HDFS-7430:
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It is fair to call this a rewrite of major parts of the block scanner.
I don't think it makes sense to maintain two block scanners in parallel. There
would have to be a lot of glue code and extra interfaces to get both working.
Let's let this soak in trunk for a while and then merge to branch-2 when it is
stabilized, the same as we did with other things such as truncate.
> Refactor the BlockScanner to use O(1) memory and use multiple threads
> ---------------------------------------------------------------------
>
> Key: HDFS-7430
> URL: https://issues.apache.org/jira/browse/HDFS-7430
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.7.0
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Attachments: HDFS-7430.002.patch, HDFS-7430.003.patch,
> HDFS-7430.004.patch, HDFS-7430.005.patch, HDFS-7430.006.patch,
> HDFS-7430.007.patch, HDFS-7430.008.patch, HDFS-7430.009.patch,
> HDFS-7430.010.patch, HDFS-7430.011.patch, HDFS-7430.012.patch, memory.png
>
>
> We should update the BlockScanner to use a constant amount of memory by
> keeping track of what block was scanned last, rather than by tracking the
> scan status of all blocks in memory. Also, instead of having just one
> thread, we should have a verification thread per hard disk (or other volume),
> scanning at a configurable rate of bytes per second.
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