perf(session): Avoid select when canceling session

[tmessi]

When a resource relating to a session is deleted,
notably a target, host, or auth_token, the corresponding sessions are
marked as canceled via a database trigger that calls the cancel_session
function. This function was performing a select as part of the insert
call to ensure that it would not attempt to insert a session_sate of
canceled if it was an invalid state transition. However, since this
function was first introduced, there has been additional constraints
added that would prevent an invalid state transition. In addition,
performing a select as part of an insert increases the chances for
contention with other queries that interact with the session_state
table, especially since a large number of sessions and session_state
rows can be included in a single transaction when things like
auth_tokens or targets get deleted.

Now, the cancel_function will perform the insert, and catch any of the
potential violations, allowing the query to continue without needing to
perform the select, thus reduction the potential for contention.

[github-actions]

Database schema diff between main and tmessi-session-cancel-trigger @ 91fff8e

To understand how these diffs are generated and some limitations see the
documentation of the script.

Functions

diff --git a/.schema-diff/funcs_37bf59243a7a67fdb19ce942cde425301ed8eb12/cancel_session.sql b/.schema-diff/funcs_aef96cd9331c0ddfacec56532e63a298213c36a1/cancel_session.sql
index b685e5be6..98c8d5624 100644
--- a/.schema-diff/funcs_37bf59243a7a67fdb19ce942cde425301ed8eb12/cancel_session.sql
+++ b/.schema-diff/funcs_aef96cd9331c0ddfacec56532e63a298213c36a1/cancel_session.sql
@@ -23,31 +23,20 @@ set row_security = off;
 create function public.cancel_session(sessionid text) returns void
     language plpgsql
     as $$
-declare
-  rows_affected numeric;
-begin
-  insert into session_state(session_id, state)
-  select
-    sessionid::text, 'canceling'
-  from
-    session s
-  where
-      s.public_id = sessionid::text and
-      s.public_id not in (
-      select
-        session_id
-      from
-        session_state
-      where
-          session_id = sessionid::text and
-          state in('canceling','terminated')
-    ) limit 1;
-  get diagnostics rows_affected = row_count;
-  if rows_affected > 1 then
-    raise exception 'cancel session: more than one row affected: %', rows_affected;
-  end if;
-end;
-$$;
+  declare
+    rows_affected numeric;
+  begin
+    insert into session_state(session_id, state)
+         values              (sessionid,  'canceling');
+  exception when unique_violation
+              or foreign_key_violation
+              or check_violation
+            then
+    -- do nothing. any one of these violations would indicate that the session
+    -- either already is canceled, or is in a terminated state and cannot
+    -- be canceled.
+  end;
+  $$;
 
 
 --

Tables

Unchanged

Views

Unchanged

Triggers

Unchanged

Indexes

Unchanged

Constraints

Unchanged

Foreign Key Constraints

Unchanged

[louisruch]

LGTM