Refresh project authorizations using a Redis leaserefresh-authorizations-with-lease

When I proposed using serializable transactions I was hoping we would be
able to refresh data of individual users concurrently. Unfortunately
upon closer inspection it was revealed this was not the case. This could
result in a lot of queries failing due to serialization errors,
overloading the database in the process (given enough workers trying to
update the target table).

To work around this we're now using a Redis lease that is cancelled upon
completion. This ensures we can update the data of different users
concurrently without overloading the database.

The code will try to obtain the lease until it succeeds, waiting at
least 1 second between retries. This is necessary as we may otherwise
end up _not_ updating the data which is not an option.

1 files changed, 15 insertions, 21 deletions

diff --git a/app/models/user.rb b/app/models/user.rb
index 513a19d81d2..ad4b4d9381b 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -445,27 +445,21 @@ class User < ActiveRecord::Base
   end
 
   def refresh_authorized_projects
-    loop do
-      begin
-        Gitlab::Database.serialized_transaction do
-          project_authorizations.delete_all
-
-          # project_authorizations_union can return multiple records for the same project/user with
-          # different access_level so we take row with the maximum access_level
-          project_authorizations.connection.execute <<-SQL
-            INSERT INTO project_authorizations (user_id, project_id, access_level)
-            SELECT user_id, project_id, MAX(access_level) AS access_level
-            FROM (#{project_authorizations_union.to_sql}) sub
-            GROUP BY user_id, project_id
-          SQL
-
-          update_column(:authorized_projects_populated, true) unless authorized_projects_populated
-        end
-
-        break
-      # In the event of a concurrent modification Rails raises StatementInvalid.
-      # In this case we want to keep retrying until the transaction succeeds
-      rescue ActiveRecord::StatementInvalid
+    transaction do
+      project_authorizations.delete_all
+
+      # project_authorizations_union can return multiple records for the same
+      # project/user with different access_level so we take row with the maximum
+      # access_level
+      project_authorizations.connection.execute <<-SQL
+      INSERT INTO project_authorizations (user_id, project_id, access_level)
+      SELECT user_id, project_id, MAX(access_level) AS access_level
+      FROM (#{project_authorizations_union.to_sql}) sub
+      GROUP BY user_id, project_id
+      SQL
+
+      unless authorized_projects_populated
+        update_column(:authorized_projects_populated, true)
       end
     end
   end