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https://issues.apache.org/jira/browse/HBASE-6233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13396133#comment-13396133
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Matteo Bertozzi commented on HBASE-6233:
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Taking a snapshot means keeping references to hfiles currently present in the
table.
Unfortunately during compaction and split these file can be removed from the
original location.
One solution can be:
* move hfiles to .snapshot/files directory, during the "take snapshot"
operation
* create symlinks to .snapshot/files in the table folder.
* create the snapshot reference in .snapshot/name/files
This allows to restore snapshot easily by creating a symlink.
The hbase code will not change since compaction can still call fs.delete() and
ends up deleting just the symlink
One problem is that during the fs.rename() + fs.createSymlink() the filename is
not available and if DFSInputStream.callGetBlockLocations() is called you end
up with a FileNotFoundException.
_But this means that after a snapshot the files in the table folder are
symlink, so you'll see both normal files + symlink during the table life._
> [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
>
> 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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