> Ok... it's really strange to me that Cassandra doesn't support data > versioning cause all of other key-value databases support it (at least > those who I know). You can design it into your data model if you need it. > I have one remaining question: > -in the case that I have more than 1 SSTable in the disk for the same > column but with different data versions, is it possible to make a > query to get the old version instead of the newest one? No. There is only ever 1 value for a column. The "older" copies of the column in the SSTables are artefacts of immutable on disk structures. If you want to see what's inside an SSTable use bin/sstable2json
Cheers ----------------- Aaron Morton Freelance Developer @aaronmorton http://www.thelastpickle.com On 24/05/2012, at 9:42 PM, Felipe Schmidt wrote: > Ok... it's really strange to me that Cassandra doesn't support data > versioning cause all of other key-value databases support it (at least > those who I know). > > I have one remaining question: > -in the case that I have more than 1 SSTable in the disk for the same > column but with different data versions, is it possible to make a > query to get the old version instead of the newest one? > > Regards, > Felipe Mathias Schmidt > (Computer Science UFRGS, RS, Brazil) > > > > > 2012/5/16 Dave Brosius <dbros...@mebigfatguy.com>: >> 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) >>>> >>>> >>>> >>
