Right now CDC is very very LOW LEVEL, you'll need to 1. Use a CommitLogReader to read the changes from the CDC files 2. Perform de-duplication by yourself
I'll blog post a technical deep dive about CDC in the future once I have time to play with it On Mon, Dec 19, 2016 at 9:57 PM, Oren Yekutieli <oren.yekuti...@ecitele.com> wrote: > Thank you both Matija and Eric. > > I have read somewhere about CDC but I didn’t know that it is already > released. > > I also didn’t find good documentation of it except for the design doc and > Jira ticket, where in both cases it is hard to know what really was > released. > > As a newbie to Cassandra I will probably do need a more ‘user friendly’ > CDC documentation. Is it available somewhere? > > > > Regards, > > Oren > > > > *From:* Eric Stevens [mailto:migh...@gmail.com] > *Sent:* Saturday, December 17, 2016 12:32 AM > *To:* user@cassandra.apache.org > *Subject:* Re: FW: Cassandra trigger to send notifications > > > > You probably want to look at change data capture rather than triggers: > http://cassandra.apache.org/doc/latest/operating/cdc.html > > Be aware that one of your criteria regarding operation order is going to > be very difficult to guarantee due to eventual consistency. > > > > On Fri, Dec 16, 2016, 2:43 AM Matija Gobec <matija0...@gmail.com> wrote: > > Hi Oren, > > > > I've spent a reasonable time working out triggers and I would say that > your best bet is doing this in the app. > > Just publish a rabbitmq message from the app when you execute a statement. > > If your goal is to have an audit then try batch writing data to the tables > and delta to their audit counterparts. > > > > Matija > > > > On Fri, Dec 16, 2016 at 9:14 AM, Oren Yekutieli < > oren.yekuti...@ecitele.com> wrote: > > Hello, > > > > In a Cassandra cluster I want to push a notification to rabbitmq whenever > a change (insert/update/delete) was made to some Cassandra tables, with the > following requirements: > > The notifications should: > > 1. Be ordered in the same order the changes were stored. > > 2. Be sent only if the change was (or going to be) committed > successfully. > > And in case of insert/update: > > 3. Include all the row values. > > 4. Indicate what values were changed. > > > > I’m trying to figure out if Cassandra triggers are the correct way to go. > > According to http://www.datastax.com/dev/blog/whats-new-in-cassandra-2- > 0-prototype-triggers-support, one of the potential use cases for triggers > is: > > · >> implementing alerts/notifications > > I also played a bit with the example given here: http://stackoverflow.com/ > questions/35161747/example-of-creating-triggers-in- > cassandra-and-does-this-support-only-for-java and from what I read and > learned so far I assume that: > > Regarding #1, I doubt if the notification order can be kept since the > trigger is invoked on the coordinator node while there are multiple clients > that can connect to the various cluster nodes (coordinators). > > Regarding #2, I’m not sure that notification will be sent only for changes > that are going to be committed successfully since the trigger is invoked > before the change is being applied. > > Regarding #3, I seen that this requirement is fulfilled. > > Regarding #4, I didn’t find a way to figure out what values are actually > changed, without re-reading the current (old) values from the table which > of course impose a significant performance penalty. > > > > Are my assumptions correct? > > If yes then triggers are not the right approach. What other ways can be > taken? > > > > Regards, > > Oren > > > > > >
