Postgres 9 how to drop a database that is in-use

PostgreSQL's statistics collector is a subsystem that supports collection and reporting of information about server activity

Sample below to identify the procid for database cmdbuild:

postgres=# select * from pg_stat_activity where datname='cmdbuild';

datid	datname	procpid	usesysid
44867	cmdbuild	2467	16384
44867	cmdbuild	2468	16384

(2 rows)

pg_cancel_backend and pg_terminate_backend send signals (SIGINT or SIGTERM respectively) to backend processes identified by process ID. 

postgres=# select pg_terminate_backend(procpid) from pg_stat_activity where datname='cmdbuild';

 pg_terminate_backend 

----------------------

 t

 t

(2 rows)

postgres=# DROP DATABASE cmdbuild;

DROP DATABASE