only try to cancel open connections

core/dbt/adapters/sql/connections.py

@@ -6,7 +6,7 @@
 
 import dbt.clients.agate_helper
 import dbt.exceptions
-from dbt.contracts.connection import Connection
+from dbt.contracts.connection import Connection, ConnectionState
 from dbt.adapters.base import BaseConnectionManager
 from dbt.logger import GLOBAL_LOGGER as logger
 
@@ -37,7 +37,10 @@ def cancel_open(self) -> List[str]:
 
                 # if the connection failed, the handle will be None so we have
                 # nothing to cancel.
-                if connection.handle is not None:
+                if (
+                    connection.handle is not None and
+                    connection.state == ConnectionState.OPEN
+                ):
                     self.cancel(connection)
                 if connection.name is not None:
                     names.append(connection.name)

plugins/postgres/dbt/adapters/postgres/connections.py

@@ -121,7 +121,17 @@ def open(cls, connection):
 
     def cancel(self, connection):
         connection_name = connection.name
-        pid = connection.handle.get_backend_pid()
+        try:
+            pid = connection.handle.get_backend_pid()
+        except psycopg2.InterfaceError as exc:
+            # if the connection is already closed, not much to cancel!
+            if 'already closed' in str(exc):
+                logger.debug(
+                    f'Connection {connection_name} was already closed'
+                )
+                return
+            # probably bad, re-raise it
+            raise
 
         sql = "select pg_terminate_backend({})".format(pid)