Can someone point me to a detailed documentation how paging is implemented, with page and page state? I have gone through https://datastax.github.io/java-driver/manual/paging/
But how is it implemented internally?
Is the coordinator drawing data and does a limit offset query as the data is drawn out from replicas sequentially for every page request?
Or are the saving the file cursor and doing a RandomAccess? If so can I get that back from the driver and use it later on?
The documentation you mentioned is the most up-to-date about pagination with the DataStax Java driver. You can also read this blog post, which is a bit old, but still valid.
Is the coordinator drawing data and does a limit offset query [...] ?
No. Actually, there is no "offset query" in Cassandra, see CASSANDRA-6511. This is also covered in the driver documentation on paging.
Or are the saving the file cursor and doing a RandomAccess? If so can I get that back from the driver and use it later on?
Yes to both. The paging state exposed by the driver is meant to be used in exactly that way; again, this is explained in the driver documentation on paging.
