Improve a query that terminates compeling backends from citus_update_node() (#6468)
Improve a query that terminates compeling backends from citus_update_node() (#6468)

DESCRIPTION: Improve a query that terminates compeling backends from citus_update_node()

1. Use pg_blocking_pids() function instead of self join on pg_locks. It exists since 9.6 and more accurate than pg_locks.
2. Prefix all function calls with pg_catalog schema to prevent privilege escalation by creating functions with similar names in a public schema.
3. Change logs and update comments to reflect the fact that the pg_terminate_backend() function only sends SIGTERM but not wating for the actual backend termination.
citusdata/citus,citusdata/citus,citusdata/citus,citusdata/citus,citusdata/citus