Hi, You do not need to have 700 Go of data in RAM. Cassandra is able to store on disks and query from there if data is not cached in memory. Caches are maintained by C* by itself but you still have to some configuration.
Supposing you want to store around 800 Go and with a RF=3, you will need at least 6 servers if you want to store all data of your db (keeping max 400 Go per server) : 800x3/400=6. There is no native implementation of trigger in C*. Anyway, there is an extension bringing this feature: https://github.com/hmsonline/cassandra-triggers. This should allow you to be notified of mutations (ie: not query). Some peoples on this ML are involved in this, maybe they could help on this. Cheers, - Pierre -----Original Message----- From: Oliver Plohmann <oli...@objectscape.org> Date: Sun, 12 Aug 2012 21:24:43 To: <user@cassandra.apache.org> Reply-To: user@cassandra.apache.org Subject: Loading data on-demand in Cassandra Hello, I'm looking a bit into Cassandra to see whether it would be something to go with for my company. I searched through the Internet, looked through the FAQs, etc. but there are still some few open questions. Hope I don't bother anybody with the usual beginner questions ... Is there a way to do load-on-demand of data in Cassandra? For the time being, we cannot afford to built up a cluster that holds our 700 GB SQL-Database in RAM. So we need to be able to load data on-demand from our relational database. Can this be done in Cassandra? Then there also needs to be a way to unload data in order to reclaim RAM space. Would be nice if it were possible to register for an asynchronous notification in case some value was changed. Can this be done? Thanks for any answers. Regards, Oliver
