The number of connections that are allowed to the database is usually not effectively limited (I believe the default limit is currently around 64K).
Since sessions are not actively doing anything most of the time (seen from the indexserver perspective) there can be many more sessions connected to the system at the same time than there are worker threads.
As SAP HANA really is a single-process-many-threads design, the connection/session handling is very much closer to e.g. Oracle's SHARED SERVER approach than to what is usually done with NetWeaver on Oracle (1:1 relation workprocess to "shadow"-process on db level).
When you're talking about COMMIT you have to distinguish between the ABAP command COMMIT WORK (or an implicit COMMIT WORK) and the DB command COMMMIT.
On all DBMS platforms those work very differently and the SAP NetWeaver Updater process decouples these two concepts.
That's not specific to SAP HANA though.
- Lars