I have further questions: -Is there any other way to stract the contect of SSTable, writing a java program for example instead of using sstable2json? -I tried to get tombstons using the thrift API, but seems to be not possible, is it right? When I try, the program throws an exception.
thanks in advance Regards, Felipe Mathias Schmidt (Computer Science UFRGS, RS, Brazil) 2012/5/24 aaron morton <aa...@thelastpickle.com>: > 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) > > > > > >
