Optimized event pruning query to avoid two queries.

CHANGELOG

@@ -3,9 +3,8 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.12.0 (unreleased)
   - Add ability to fork to a specific namespace using API. (ritave)
   - Cleanup misalignments in Issue list view !6206
-  - Prune events older than 12 months. @ritave <olaf@tomalka.me>
+  - Prune events older than 12 months. (ritave)
   - Prepend blank line to `Closes` message on merge request linked to issue (lukehowell)
-  - Prune events older than 12 months.
   - Filter tags by name !6121
   - Make push events have equal vertical spacing.
   - Add two-factor recovery endpoint to internal API !5510

app/workers/prune_old_events_worker.rb

@@ -2,7 +2,16 @@ class PruneOldEventsWorker
   include Sidekiq::Worker
 
   def perform
-    # Contribution calendar shows maximum 12 months of events
-    Event.delete(Event.unscoped.where('created_at < ?', (12.months + 1.day).ago).limit(10_000).pluck(:id))
+    # Contribution calendar shows maximum 12 months of events.
+    # Double nested query is used because MySQL doesn't allow DELETE subqueries
+    # on the same table.
+    Event.unscoped.where(
+      '(id IN (SELECT id FROM (?) ids_to_remove))',
+      Event.unscoped.where(
+        'created_at < ?',
+        (12.months + 1.day).ago).
+      select(:id).
+      limit(10_000)).
+    delete_all
   end
 end