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From "Matteo Bertozzi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6233) [brainstorm] snapshots: hardlink alternatives
Date Sat, 07 Jul 2012 19:23:36 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13408749#comment-13408749
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Matteo Bertozzi commented on HBASE-6233:
----------------------------------------

{quote}So structural changes are needed for symlink approach to work. We should carefully
evaluate the pros and cons of maintaining this new logic.{quote}
The cleanup is needed only to remove archived hfiles used by the snapshots,
and can be an external tool or an internal thread that scan the snapshot.
Is not only for the symlink approach but for all three, with the exception for .META. refcount
that can run a fs.delete() automatically when refcount reaches zero.

(In the Jesse implementation HBASE-6055 there's already a cleanup tool implemented)
                
> [brainstorm] snapshots: hardlink alternatives
> ---------------------------------------------
>
>                 Key: HBASE-6233
>                 URL: https://issues.apache.org/jira/browse/HBASE-6233
>             Project: HBase
>          Issue Type: Brainstorming
>            Reporter: Matteo Bertozzi
>            Assignee: Matteo Bertozzi
>         Attachments: Restore-Snapshot-Hardlink-alternatives.pdf
>
>
> Discussion ticket around snapshots and hardlink alternatives.
> (See the HDFS-3370 discussion about hardlink and implementation problems)
> (taking for a moment WAL out of the discussion and focusing on hfiles)
> With hardlinks available taking snapshot will be fairly easy:
> * (hfiles are immutable)
> * hardlink to .snapshot/name to take snapshot
> * hardlink from .snapshot/name to restore the snapshot
> * No code change needed (on fs.delete() only one reference is deleted)
> but we don't have hardlinks, what are the alternatives?

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