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From "Pierre Chalamet" <>
Subject Re: Loading data on-demand in Cassandra
Date Mon, 13 Aug 2012 07:12:42 GMT

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: 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.


- Pierre

-----Original Message-----
From: Oliver Plohmann <>
Date: Sun, 12 Aug 2012 21:24:43 
To: <>
Subject: Loading data on-demand in Cassandra


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

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