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From "HBase Review Board (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-50) Snapshot of table
Date Wed, 11 Aug 2010 05:15:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-50?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12897144#action_12897144
] 

HBase Review Board commented on HBASE-50:
-----------------------------------------

Message from: "Chongxin Li" <lichongxin@zju.edu.cn>


bq.  On 2010-08-10 10:04:44, Ted Yu wrote:
bq.  > src/main/java/org/apache/hadoop/hbase/master/HMaster.java, line 962
bq.  > <http://review.cloudera.org/r/467/diff/3/?file=6015#file6015line962>
bq.  >
bq.  >     It would be better to move crashed snapshots into a separate directory under
snapshot rootDir.

If so, probably we need the above method.
But why move crashed snapshots into a separate directory? It would be pretty hard to recover
a crashed snapshot.


bq.  On 2010-08-10 10:04:44, Ted Yu wrote:
bq.  > src/main/java/org/apache/hadoop/hbase/master/HMaster.java, line 945
bq.  > <http://review.cloudera.org/r/467/diff/3/?file=6015#file6015line945>
bq.  >
bq.  >     If you create directory for failed snapshots, you can also add listFailedSnapshots()
method.

Currently there is no directory for failed snapshots. If snapshot fails, it is cleaned up
and exception is thrown to notify the user.


bq.  On 2010-08-10 10:04:44, Ted Yu wrote:
bq.  > src/main/java/org/apache/hadoop/hbase/master/HMaster.java, line 930
bq.  > <http://review.cloudera.org/r/467/diff/3/?file=6015#file6015line930>
bq.  >
bq.  >     Do we need to abort TableSnapshot processing in case of exception ?

For snapshot which is created by TableSnapshot, the table must be offline and snapshot is
totally driven by the master. Region servers have no awareness of such a snapshot. So in case
of exception, just clean up the failed snapshot. There is no need to abort the snapshot across
the cluster.

Regarding SnapshotMonitor, it only monitors the snapshots which are created across the region
servers.


- Chongxin


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> Snapshot of table
> -----------------
>
>                 Key: HBASE-50
>                 URL: https://issues.apache.org/jira/browse/HBASE-50
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Billy Pearson
>            Assignee: Li Chongxin
>            Priority: Minor
>         Attachments: HBase Snapshot Design Report V2.pdf, HBase Snapshot Design Report
V3.pdf, HBase Snapshot Implementation Plan.pdf, Snapshot Class Diagram.png
>
>
> Havening an option to take a snapshot of a table would be vary useful in production.
> What I would like to see this option do is do a merge of all the data into one or more
files stored in the same folder on the dfs. This way we could save data in case of a software
bug in hadoop or user code. 
> The other advantage would be to be able to export a table to multi locations. Say I had
a read_only table that must be online. I could take a snapshot of it when needed and export
it to a separate data center and have it loaded there and then i would have it online at multi
data centers for load balancing and failover.
> I understand that hadoop takes the need out of havening backup to protect from failed
servers, but this does not protect use from software bugs that might delete or alter data
in ways we did not plan. We should have a way we can roll back a dataset.

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