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From aaron morton <aa...@thelastpickle.com>
Subject Re: how to take consistant snapshot?
Date Fri, 07 Dec 2012 03:34:30 GMT
For background

http://wiki.apache.org/cassandra/Operations?highlight=%28snapshot%29#Consistent_backups

If you it for a single node then yes there is a chance of inconsistency across CF's. 

If you have mulitple nodes the snashots you take on the later nodes will help. If you use
CL QUOURM for reads you *may* be ok (cannot work it out quickly.). If you use CL ALL for reads
you will be ok. Or you can use nodetool repair to ensure the data is consistent. 

I doubt that even using repair would give you a provable guarantee though. Anyone ?

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 6/12/2012, at 7:56 AM, Andrey Ilinykh <ailinykh@gmail.com> wrote:

> Hello, everybody!
> I have production cluster with incremental backup on and I want to clone it (create test
one). I don't understand one thing- each column family gets flushed (and copied to backup
storage) independently. Which means the total snapshot is inconsistent. If I restore from
such snapshot  I have totally useless system. To be more specific, let's say I have two CF,
one serves as an index for another. Every time I update one CF I update index CF. There is
a good chance that all replicas flush index CF first. Then I move it into backup storage,
restore and get CF which has pointers to non existent data in another CF. What is a way to
avoid this situation?
> 
> Thank you,
>   Andrey


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