PostgreSQL is used for various things in a dCache system: The SRM, the pin manager, the space manager, the replica manager, the pnfs companion, the billing, and the pnfs server might make use of one or more databases in a single or several separate PostgreSQL servers.

The SRM, the pin manager, the space manager, the replica manager, and the pnfs companion will use the PostgreSQL database as configured at cell start-up in the corresponding batch files. The billing will only write the accounting information into a database if it is configured with the option -useSQL. The pnfs server will use a PostgreSQL server if the pnfs-posgresql version is used. It will use several databases in the PostgreSQL server, just as the gdbm version of the pnfs server uses serveral database files. How to convert the gdbm files of an existing pnfs server into PostgreSQL databases is described in Chapter 20, Moving the pnfs Data from GDBM to PostgreSQL.