There are several types of process models that's suitable for a DBMS: 1 process per DBMS worker, 1 thread per DBMS worker, a lightweight thread pool, a process

There are several types of process models that's suitable for a DBMS: 1 process per DBMS worker, 1 thread per DBMS worker, a lightweight thread pool, a process pool, etc. Hellerstein, Stonebraker and Hamilton (2007) is a great introduction on this.