I use the "db2 get snapshot for all on zmccdb" to get the following information:
Database name = ZMCCDB
Database path = /home/zmccinst/zmccdb/db2inst2/NODE0000/SQL00001/
Input database alias = ZMCCDB
Database status = Active
Catalog database partition number = 0
Catalog network node name =
Operating system running at database server= AIX
Location of the database = Local
First database connect timestamp = 07-13-2004 21:00:52.200086
Last reset timestamp =
Last backup timestamp = 08-01-2004 21:00:42.086460
Snapshot timestamp = 08-02-2004 17:52:43.010177

High water mark for connections = 21
Application connects = 1331
Secondary connects total = 0
Applications connected currently = 7
Appls. executing in db manager currently = 0
Agents associated with applications = 7
Maximum agents associated with applications= 21
Maximum coordinating agents = 21

I want to know the meanings of "High water mark for connections" and "Application connects " and "Applications connected currently ".
Also ,please tell me how to get the session number just like in oracle
Thanks

High water mark - maximum number of connections to the database that were active at any time after the monitor was last reset.

Application connects - number of connection attempts (I think).

Applications connected currently - that's sort of obvious, isn't it?

This probably gives you the same as "select count(*) from v$session" in Oracle.

To list all connected applications (what you refer to as "Sessions" in Oracle) use "list applications [show detail]".