Add Terminating A Connection as a postgres til

postgres/terminating-a-connection.md

@@ -0,0 +1,42 @@
+# Terminating A Connection
+
+Consider the scenario where you are trying to drop a database, but there are
+existing connections.
+
+```bash
+$ dropdb sample_db
+dropdb: database removal failed: ERROR:  database "sample_db" is being accessed by other users
+DETAIL:  There is 1 other session using the database.
+```
+
+If you don't know where these connections are, you can terminate them within
+a `psql` session. You just have to figure out the `pid` of those
+connections. In [List Connections To A
+Database](postgres/list-connections-to-a-database.md), I explained how to
+get at the `pid` values of connections. Using the `pid` value, you can
+terminate a connection.
+
+```sql
+> select pg_terminate_backend(12345);
+ pg_terminate_backend
+----------------------
+ t
+```
+
+To terminate all connections to a particular database, use a query like the
+following:
+
+```sql
+select pg_terminate_backend(pg_stat_activity.pid)
+from pg_stat_activity
+where pg_stat_activity.datname = 'test_drop'
+  and pid <> pg_backend_pid();
+ pg_terminate_backend
+----------------------
+ t
+```
+
+This excludes the current session, so you'll need to exit `psql` as well
+before dropping the database.
+
+[source](http://stackoverflow.com/questions/5408156/how-to-drop-a-postgresql-database-if-there-are-active-connections-to-it)