That's a good approach. You could also migrate in-place if you're confident your migration algorithm is correct, but for more safety having another CF is better.
If you have a huge volume of data to be migrated (millions of rows or more), I'd suggest you to use Hadoop to perform these migrations ( http://wiki.apache.org/cassandra/HadoopSupport). If it's only a few rows, then you could do it programmatically via * get_range_slices* using the language binding of your choice. Below are some links on how to perform this on Hector or Pycassa: * Hector: http://stackoverflow.com/questions/8418448/cassandra-hector-how-to-retrieve-all-rows-of-a-column-family * Pycassa: http://pycassa.github.io/pycassa/api/pycassa/columnfamily.html#pycassa.columnfamily.ColumnFamily.get_range I Agree with Edward that you should only delete the rows once you make sure they were correctly migrated. 2013/9/7 Edward Capriolo <edlinuxg...@gmail.com> > I would do something like you are suggesting. I would not do the delete > until all the rows are moved. Since writes in cassandra are idempotent you > can even run the migration process multiple times without harm. > > > On Sat, Sep 7, 2013 at 5:31 PM, Renat Gilfanov <gren...@mail.ru> wrote: > >> Hello, >> >> Let's say we have a simple CQL3 table >> >> CREATE TABLE example ( >> id UUID PRIMARY KEY, >> timestamp TIMESTAMP, >> data ASCII >> ); >> >> And I need to mutate (for example encrypt) column values in the "data" >> column for all rows. >> >> What's the recommended approach to perform such migration >> programatically? >> >> For me the general approach is: >> >> 1. Create another column family >> 2. extract a batch of records >> 3. for each extracted record, perform mutation, insert it in the new cf >> and delete from old one >> 4. repeat until source cf not empty >> >> Is it correct approach and if yes, how to implement some kind of paging >> for the step 2? >> > > -- Paulo Ricardo -- European Master in Distributed Computing*** Royal Institute of Technology - KTH * *Instituto Superior Técnico - IST* *http://paulormg.com*
