Hi Santosh, Redis is used for a number of different things:
It's used for storing and retrieving session information. This is needed for every request and we needed this to be as light-weight as possible. On top of that, an out-of-the-box Redis session store implementation was already available. We are using the Redis PubSub [1] feature to provide cluster-wide communication between app servers. For example, this makes it possible to inform all app servers that an Admin UI configuration change has been made, allowing for all app servers to re-cache that information. Redis is also used as our activity aggregation store [2]. Activity aggregation is an intensive operation, and is something that is required a lot. Cassandra could have been used for this, but Redis produced better performance testing results. This is to be expected as Redis doesn't persist to disk. If we lose the aggregation data, aggregate-able activities won't be aggregated for a short period of time, but this doesn't result in any data loss. So even though Redis isn't used as a canonical data source, it is being used for a number of different goals. Therefore, it is currently not possible to run OAE with Cassandra only. [1] http://redis.io/topics/pubsub [2] https://confluence.sakaiproject.org/display/3AK/Activities#Activities-Aggregation Hope that helps, Nicolaas On 5 Aug 2013, at 07:47, Santosh Kumar wrote: > Hi friends, > > I wanted to know why we are using both cassandra and redis . > Can we use only cassandra instead of Redis > > > -- > Regards > ---- > > Santosh Kumar C S > 8553631248 > >
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