Remove support for sticking to old and new keys

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/67773 we added
support for multiple databases in the load balancer. This was released
in 14.4. As part of these changes, we added support for reading/writing
to both the old and new Redis keys, making it easier to switch between
the old and new version of the code.

In this commit we remove the use of the old key format, as it's no
longer needed.

This fixes https://gitlab.com/gitlab-org/gitlab/-/issues/345208

Changelog: changed

lib/gitlab/database/load_balancing/sticking.rb

@@ -123,21 +123,18 @@ module Gitlab
         def unstick(namespace, id)
           Gitlab::Redis::SharedState.with do |redis|
             redis.del(redis_key_for(namespace, id))
-            redis.del(old_redis_key_for(namespace, id))
           end
         end
 
         def set_write_location_for(namespace, id, location)
           Gitlab::Redis::SharedState.with do |redis|
             redis.set(redis_key_for(namespace, id), location, ex: EXPIRATION)
-            redis.set(old_redis_key_for(namespace, id), location, ex: EXPIRATION)
           end
         end
 
         def last_write_location_for(namespace, id)
           Gitlab::Redis::SharedState.with do |redis|
-            redis.get(redis_key_for(namespace, id)) ||
-              redis.get(old_redis_key_for(namespace, id))
+            redis.get(redis_key_for(namespace, id))
           end
         end
 
@@ -146,10 +143,6 @@ module Gitlab
 
           "database-load-balancing/write-location/#{name}/#{namespace}/#{id}"
         end
-
-        def old_redis_key_for(namespace, id)
-          "database-load-balancing/write-location/#{namespace}/#{id}"
-        end
       end
     end
   end

spec/lib/gitlab/database/load_balancing/sticking_spec.rb

@@ -256,15 +256,6 @@ RSpec.describe Gitlab::Database::LoadBalancing::Sticking, :redis do
 
       expect(sticking.last_write_location_for(:user, 4)).to be_nil
     end
-
-    it 'removes the old key' do
-      Gitlab::Redis::SharedState.with do |redis|
-        redis.set(sticking.send(:old_redis_key_for, :user, 4), 'foo', ex: 30)
-      end
-
-      sticking.unstick(:user, 4)
-      expect(sticking.last_write_location_for(:user, 4)).to be_nil
-    end
   end
 
   describe '#last_write_location_for' do
@@ -273,14 +264,6 @@ RSpec.describe Gitlab::Database::LoadBalancing::Sticking, :redis do
 
       expect(sticking.last_write_location_for(:user, 4)).to eq('foo')
     end
-
-    it 'falls back to reading the old key' do
-      Gitlab::Redis::SharedState.with do |redis|
-        redis.set(sticking.send(:old_redis_key_for, :user, 4), 'foo', ex: 30)
-      end
-
-      expect(sticking.last_write_location_for(:user, 4)).to eq('foo')
-    end
   end
 
   describe '#redis_key_for' do