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Date: Mon, 11 Jun 2012 15:58:44 +0000 (UTC)
From: "Jonathan Hsieh (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HBASE-6055) Snapshots in HBase 0.96
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    [ https://issues.apache.org/jira/browse/HBASE-6055?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13292852#comment-13292852 ] 

Jonathan Hsieh commented on HBASE-6055:
---------------------------------------

I still a bit confused -- still at the basic admin level.  I think it would help if we give the "restoring"/"export" parts some more attention and talk about usage as opposed to mechanism first.  I'm going to pose some use case/examples/scenarios which hopefully will be easier to discuss.  

Let's say I am an admin, and we are pre hdfs hardlinks.  

I issue a "snapshot" command at the shell/master.  
* HBase creates a new .snapshot subdir, and it contains references to HLogs and HFiles.  This is a "snapshot"
** This step is called: snapshotting, "taking a snapshot", and also materializing right?

I currently have a snapshot.  I want read-only access its contents to compare with the current table.
* Does HBase know how to interpret the stuff in a .snapshot dir such that it act like a read-only table?
* Do I, as an admin, need to execute some step to make it appear in HBase as a read-only table? (if so what is this called?)

I currently have a snapshot.  Oops! I accidentally truncated the table I had snapshotted.  I don't want the truncated version of the table anymore and I want to replace the table with the snapshot so I have read write access.
* This is called "restoring" the snapshot right? (and I do this by issuing a something like "restore" command at the shell?)
* Does HBase copy or move the data referred to in the snapshot? 

I currently have a snapshot.  I want the current version but I'd like to clone of the snapshotted table that provides read/write access to the clone.
* Is/should this be supported?
* Is this called "restoring" or "exporting" the snapshot (to a new name)?
* For this to work I need to convert all references into actual copies of the HFiles and HLogs right?  Is this conversion called exporting? (FYI, this is what I meant materializing to mean, but let's just stick to your definitions)

I currently have a snapshot.  I want to send a copy of the snapshot to a remote cluster so that it can provide read/write access to the data.  
* Is/should this be supported?
* Do both HBase instances need to be up at the same time? 
** This process would need to dereference the snapshot's references and copy them.  What is it called?  exporting?


----
Source of confusion

bq. Export is taking a snapshot from the .snapshot/ directory and possibly having a special snapshot distcp to somewhere. I would consider materialization as taking the exported snapshot and then 'hooking it back up' to another cluster (or the same) as a new table. You could throw materialization of the exported snapshot, but they are in fact distinct.

I think the first "materialization" is supposed to be "restoration" yeah?  I don't quite get the last sentence.

                
> Snapshots in HBase 0.96
> -----------------------
>
>                 Key: HBASE-6055
>                 URL: https://issues.apache.org/jira/browse/HBASE-6055
>             Project: HBase
>          Issue Type: New Feature
>          Components: client, master, regionserver, zookeeper
>            Reporter: Jesse Yates
>            Assignee: Jesse Yates
>             Fix For: 0.96.0
>
>         Attachments: Snapshots in HBase.docx
>
>
> Continuation of HBASE-50 for the current trunk. Since the implementation has drastically changed, opening as a new ticket.

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