Here is my answer to very similar question on StackOverflow.

Depending on your version of postgresql you might run into a bug, that makes pg_stat_activity to omit active connections from dropped users. These connections are also not shown inside pgAdminIII.

If you are doing automatic testing (in which you also create users) this might be a probable scenario.

In this case you need to revert to queries like:

 SELECT pg_terminate_backend(pg_stat_activity.procpid) 
 FROM pg_stat_get_activity(NULL::integer) 
 WHERE datid=(SELECT oid from pg_database where datname = 'your_database');

Here is my answer to very similar question on StackOverflow.

Depending on your version of postgresql you might run into a bug, that makes pg_stat_activity to omit active connections from dropped users. These connections are also not shown inside pgAdminIII.

If you are doing automatic testing (in which you also create users) this might be a probable scenario.

In this case you need to revert to queries like:

 SELECT pg_terminate_backend(pg_stat_activity.procpid) 
 FROM pg_stat_get_activity(NULL::integer) 
 WHERE datid=(SELECT oid from pg_database where datname = 'your_database');