Pause Sidekiq when postgres failovers.

lib/active_record/connection_adapters/postgresql_fallback_adapter.rb

@@ -32,7 +32,10 @@ class PostgreSQLFallbackHandler
   end
 
   def master_down=(args)
-    synchronize { @masters_down[namespace] = args }
+    synchronize do
+      @masters_down[namespace] = args
+      Sidekiq.pause! if args
+    end
   end
 
   def master_up(namespace)
@@ -53,6 +56,7 @@ class PostgreSQLFallbackHandler
 
             self.master_up(key)
             Discourse.disable_readonly_mode(Discourse::PG_READONLY_MODE_KEY)
+            Sidekiq.unpause!
           end
         rescue => e
           logger.warn "#{log_prefix}: Connection to master PostgreSQL server failed with '#{e.message}'"

spec/components/active_record/connection_adapters/postgresql_fallback_adapter_spec.rb

@@ -71,6 +71,7 @@ describe ActiveRecord::ConnectionHandling do
           .to change { Discourse.readonly_mode? }.from(false).to(true)
 
         expect(postgresql_fallback_handler.master_down?).to eq(true)
+        expect(Sidekiq.paused?).to eq(true)
 
         with_multisite_db(multisite_db) do
           expect(postgresql_fallback_handler.master_down?).to eq(nil)
@@ -92,6 +93,7 @@ describe ActiveRecord::ConnectionHandling do
 
         expect(Discourse.readonly_mode?).to eq(false)
         expect(postgresql_fallback_handler.master_down?).to eq(nil)
+        expect(Sidekiq.paused?).to eq(false)
         expect(ActiveRecord::Base.connection_pool.connections.count).to eq(0)
 
         skip("Figuring out why the following keeps failing to obtain a connection on Travis")