Do not schedule Session.purge if the Session model is not used

You can use memcache or SQL session. When you use memcache this whole
job does nothing. Just inserts into a queue, updates queue, selects
empty from Session and then removes from queue.

This also frees up some memory and scheduler cycles. Yaix!

Note, we already require users (in documentation) to restart EVM server
when they change session store (so we can do this).

app/models/miq_schedule_worker/runner.rb

@@ -184,10 +184,12 @@ def schedules_for_scheduler_role
       enqueue :drift_state_purge_timer
     end
 
-    # Schedule - Check for session timeouts
-    scheduler.schedule_every(worker_settings[:session_timeout_interval]) do
-      # Session is global to the region, therefore, run it only once on the scheduler's server
-      enqueue :session_check_session_timeout
+    if Session.enabled?
+      # Schedule - Check for session timeouts
+      scheduler.schedule_every(worker_settings[:session_timeout_interval]) do
+        # Session is global to the region, therefore, run it only once on the scheduler's server
+        enqueue :session_check_session_timeout
+      end
     end
 
     # Schedule - Check for rogue EVM snapshots

app/models/session.rb

@@ -3,6 +3,10 @@ class Session < ApplicationRecord
   @@interval = 30 # how often to purge in seconds
   @@job ||= nil
 
+  def self.enabled?
+    ::Settings.server.session_store == 'sql'
+  end
+
   def self.check_session_timeout
     $log.debug "Checking session data"
     purge(::Settings.session.timeout)