Using Sessions in Cassandra

Question

When using cassandra datastax java driver, When can I use multiple sessions under same cluster? I am not able to find any good usecase for having a cluster and multiple sessions. My application have multiple components/modules that accesses Cassandra. Based on the answer I may decide Should I be having one session per component/module or just one session shared across all the components of my application.

Update: Everywhere on the internet they recommend to use one session. I get it, but my question is "in what scenario do you create multiple sessions for one cluster?". If there is no such scenario, why the library allows to create multiple sessions, instead the library can just have a method to return a singleton session object.

Answer 1

Use Just One Session across all your component.

Because In Cassandra Session is a heavy object. Thread-safe. It maintain multiple connection, cached prepared statement etc.

Here is the JavaDoc :

A session holds connections to a Cassandra cluster, allowing it to be queried. Each session maintains multiple connections to the cluster nodes, provides policies to choose which node to use for each query (round-robin on all nodes of the cluster by default), and handles retries for failed query (when it makes sense), etc...

Session instances are thread-safe and usually a single instance is enough per application. As a given session can only be "logged" into one keyspace at a time (where the "logged" keyspace is the one used by query if the query doesn't explicitely use a fully qualified table name), it can make sense to create one session per keyspace used. This is however not necessary to query multiple keyspaces since it is always possible to use a single session with fully qualified table name in queries.

Source :
https://docs.datastax.com/en/drivers/java/2.0/com/datastax/driver/core/Session.html https://ahappyknockoutmouse.wordpress.com/2014/11/12/246/