How Cassandra 4.0 virtual table reads data?

Question

From Documentation It is cleared that in cassandra 4.0 virtual tables are read only and no writes allowed.

Currently there are 2 vtables available i.e system_views and system_virtual_schema and it contains 17 tables.

This contains data like clients,cache ,settings etc.

Where this data is exactly coming from in vtables?

Here are all vtables: https://github.com/apache/cassandra/tree/64b338cbbce6bba70bda696250f3ccf4931b2808/src/java/org/apache/cassandra/db/virtual

PS: I have gone through cassandra.yaml Reference : https://cassandra.apache.org/doc/latest/new/virtualtables.html

Answer 1

The virtual tables store metrics data that was previously only available via JMX but now also available via CQL.

For example, the system_view.clients table tracks metadata on client connection including (but not limited to):

• the remote IP address of the client
• logged in user (if auth is enabled)
• protocol version
• driver name & version
• whether SSL is used, etc

This data is available via JMX and nodetool clientstats, and is now retrievable via CQL (I wrote about this in https://community.datastax.com/questions/6113/). Cheers!