Add Terminating A Connection as a postgres til

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_342 TILs and counting..._
+_343 TILs and counting..._
 
 ---
 
@@ -191,6 +191,7 @@ _342 TILs and counting..._
 - [String Contains Another String](postgres/string-contains-another-string.md)
 - [Temporarily Disable Triggers](postgres/temporarily-disable-triggers.md)
 - [Temporary Tables](postgres/temporary-tables.md)
+- [Terminating A Connection](postgres/terminating-a-connection.md)
 - [Timestamp Functions](postgres/timestamp-functions.md)
 - [Toggling The Pager In PSQL](postgres/toggling-the-pager-in-psql.md)
 - [Truncate All Rows](postgres/truncate-all-rows.md)

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)