Chapter on terminating queries / sessions

Author: kmoppel

61_terminating_queries.sql

@@ -0,0 +1,43 @@
+\c pg_features_demo
+SET ROLE TO demorole;
+
+/*
+
+Sometimes it is necessary to "shoot down" some own runaway queries from other users. To do that nicely from within SQL (
+technically possible also via the OS actually) there are 2 options:
+
+ * pg_cancel_backend - the nice way. Only the query gets canceled. Available for all users for their own queries.
+ * pg_terminate_backend - the hard way. User session is "kicked" from the server and needs to authenticate again. Needs
+   superuser rights or starting from v10 also possible with the "pg_signal_backend" GRANT.
+
+*/
+
+-- cancel all of your own queries from other sessions / tools
+SELECT pg_cancel_backend(pid)
+FROM pg_stat_activity
+WHERE usename = CURRENT_USER
+AND pid != pg_backend_pid();    -- always leave out our newly executing query-- cancel all of your own queries from other sessions / tools
+
+-- cancel own active queries that are running for more than 5min
+SELECT pg_cancel_backend(pid)
+FROM pg_stat_activity
+WHERE usename = CURRENT_USER
+AND state != 'idle'
+AND now() - query_start > '5min'::interval;
+
+/*
+Note though that the best way to guard against your own "runaway" queries is to set appropriate timeouts:
+*/
+SET statement_timeout TO '30s'; -- effective immediately
+ALTER ROLE demorole IN DATABASE pg_features_demo SET statement_timeout  TO '1min';  -- effective on next session
+
+-- NB! When using SET ROLE then it might be a good idea to check who you currently "are" with:
+SELECT CURRENT_USER, SESSION_USER;  -- SET ROLE alters CURRENT_USER !
+
+
+-- terminate all users that are "idling" inside of a transaction
+SELECT pg_terminate_backend(pid)
+FROM pg_stat_activity
+WHERE datname = current_database()  -- only users from "our" DB
+  AND state = 'idle in transaction'
+  AND pid != pg_backend_pid();    -- always leave out our newly executing query

todo.txt

@@ -14,5 +14,4 @@
 * PL/Pythonu
 * DO blocks
 * PG FDW
-* Sessions / killing queries
 * Information Schema