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From aaron morton <aa...@thelastpickle.com>
Subject Re: Retrieving old data version for a given row
Date Mon, 14 May 2012 20:37:37 GMT
Cassandra does not provide access to multiple versions of the same column. It is essentially
implementation detail. 

All mutations are written to the commit log in a binary format, see the o.a.c.db.RowMutation.getSerializedBuffer()
(If you want to tail it for analysis you may want to change commitlog_sync in cassandra.yaml)

Here is post about looking at multiple versions columns in an sstable http://thelastpickle.com/2011/05/15/Deletes-and-Tombstones/


Remember that not all "versions" of a column are written to disk  (see http://thelastpickle.com/2011/04/28/Forces-of-Write-and-Read/).
Also compaction will compress multiple versions of the same column from multiple files into
a single version in a single file .
  
Hope that helps. 


-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 14/05/2012, at 9:50 PM, Felipe Schmidt wrote:

> Yes, I need this information just for academic purposes.
> 
> So, to read old data values, I tried to open the Commitlog using tail
> -f and also the log files viewer of Ubuntu, but I can not see many
> informations inside of the log!
> Is there any other way to open this log? I didn't find any Cassandra
> API for this purpose.
> 
> Thanks averybody in advance.
> 
> Regards,
> Felipe Mathias Schmidt
> (Computer Science UFRGS, RS, Brazil)
> 
> 
> 
> 
> 2012/5/14 zhangcheng2 <zhangcheng2@software.ict.ac.cn>:
>> After compaciton, the old version data will gone!
>> 
>> ________________________________
>> zhangcheng2
>> 
>> From: Felipe Schmidt
>> Date: 2012-05-14 05:33
>> To: user
>> Subject: Retrieving old data version for a given row
>> I'm trying to retrieve old data version for some row but it seems not
>> be possible. I'm a beginner  with Cassandra and the unique aproach I
>> know is looking to the SSTable in the storage folder, but if I insert
>> some column and right after insert another value to the same row,
>> after flushing, I only get the last value.
>> Is there any way to get the old data version? Obviously, before compaction.
>> 
>> Regards,
>> Felipe Mathias Schmidt
>> (Computer Science UFRGS, RS, Brazil)
>> 


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