DB TIME

https://www.oracle.com/technetwork/oem/db-mgmt/s317294-db-perf-tuning-with-db-time-181631.pdf

DB TIME REPRESENTS THE TOTAL TIME :

DB TIME= DB WAIT TIME + DB CPU TIME 

Time Model

The time model is a set of statistics that give an overview of where time is spent inside the Oracle Database: 

We can check below two views for time model statistics:
V$SYS_TIME_MODEL
V$SESS_TIME_MODEL

• DB Time represents the total time.
• Spent in database calls by user sessions.
• A tuning goal is to reduce DB time.
• Using DB time, you can gauge the performance impact of any entity of the database.

Sessions:

V$SESSTAT ==>  All sessions

V$MYSTAT ==> Current session

Services:

V$SERVICE_STATS

SYSTEM:

V$SESSTAT