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From java8964 <java8...@hotmail.com>
Subject RE: Backup/Restore in Cassandra
Date Fri, 07 Mar 2014 18:30:54 GMT
Hi, Jonathan:
Thanks for your answer. My original goal of this question is not really related to backup/restore,
but to see if we can skip the Full Snapshot during ETL transferring the data from SSTable
files of Cassandra into another Hadoop Cluster.
Right now, our production generates a full snapshot once a week, and does incremental backup
every day. Our ETL implementation will parse the SSTable files, catch the delta change, and
load them into Hadoop.
Of course, the Full Snapshot is just bigger and bigger every time, so I was wondering if we
can avoid processing the snapshot, instead just the incremental backups, as it is much smaller
comparing to snapshot.
But based on currently how Cassandra does the incremental backups and snapshot, to make sure
we catch all the changed data, I think we have to process the weekly full snapshot.
Thanks
Yong

Date: Fri, 7 Mar 2014 10:33:47 -0500
Subject: Re: Backup/Restore in Cassandra
From: jlacefield@datastax.com
To: user@cassandra.apache.org

Hello,
    Full snapshot forces a flush, yes.    Incremental hard-links to SSTables, yes.
   This question really depends on how your cluster was "lost".  

   Node Loss:  You would be able to restore a node based on restoring backups + commit log
or just by using repair.   Cluster Loss: (all nodes down scenario with recoverable machines/disks):
 You would be able to restore to the point where you captured your last incremental backup.
 If you had a commit log, then those operations would be replayed during bootstrapping.  You
would also have to restore SSTables that were written to disk but not captured in an incremental
backup.
   Cluster Loss: (all nodes down scenario with unrecoverable machines/disks):  You would only
be able to restore to the last incremental backup point.  This assumes you save backups off
Cluster.

   The commit log's goal is to provide durability in case of node failure prior to a flush
operation.  The commit log will be replayed during bootstrapping a node and will repopulate
memtables.  There is also a commit log archive and restore feature as well:  http://www.datastax.com/documentation/cassandra/2.0/cassandra/configuration/configLogArchive_t.html.
 I have not personally used this feature so cannot comment on it's performance/stability.

  Does this help?
  BTW:  Here's the 1.2 documentation for backup and restore - http://www.datastax.com/documentation/cassandra/1.2/cassandra/operations/ops_backup_restore_c.html
              Here's the 2.0 documentation for backup and restore - http://www.datastax.com/documentation/cassandra/2.0/cassandra/operations/ops_backup_restore_c.html

Thanks,
Jonathan

Jonathan LacefieldSolutions Architect, DataStax
(404) 822 3487








On Thu, Mar 6, 2014 at 9:14 AM, java8964 <java8964@hotmail.com> wrote:




Hi, 
Currently I am looking how the bacup/restore be done in Cassandra, based the document from
DataStax: 
http://www.datastax.com/docs/1.1/backup_restore

Here is one way to do it:
1) Do a full snapshot every week2) Enable incremental backup every day
So with last snapshot + the incremental backups after that snapshot, you can restore the cluster
to the stage before it is lost.

Here are my understanding  how Cassandra will flush from Memtable to SSTable files in snapshot
or incremental backups:
1) Full snapshot will force Cassandra flush all memtables to SSTable files, but incremental
backup won't.
2) Incremental backup just hard-link all the SSTables after the last snapshot.
Here is my question:
If the my above understanding is correct, let's say there is a data change happened after
the last snapshot, then recorded into commit log, and stored in memtable, but never flush
to the SSTables yet, at this time, we lost our cluster. Will that change be lost just based
on last snapshot plus incremental backups? Or besides the last snapshot plus incremental backups,
we also need all commit log for a restore?

Thanks
Yong 		 	   		  

 		 	   		  
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