You're in for a world of hurt going down that rabbit hole. If you truely
want version data then you should think about changing your keying to
perhaps be a composite key where key is of form
NaturalKey/VersionId
Or if you want the versioning at the column level, use composite columns
with ColumnName/VersionId format
On 05/16/2012 10:16 AM, Felipe Schmidt wrote:
That was very helpfull, thank you very much!
I still have some questions:
-it is possible to make Cassandra keep old value data after flushing?
The same question for the memTable, before flushing. Seems to me that
when I update some tuple, the old data will be overwrited in memTable,
even before flushing.
-it is possible to scan values from the memtable, maybe using the
so-called Thrift API? Using the client-api I can just see the newest
data version, I can't see what's really happening with the memTable.
I ask that cause what I'll try to do is a Change Data Capture to
Cassandra and the answers will define what kind of aproaches I'm able
to use.
Thanks in advance.
Regards,
Felipe Mathias Schmidt
(Computer Science UFRGS, RS, Brazil)
2012/5/14 aaron morton<aa...@thelastpickle.com>:
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<zhangche...@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)
