1 files changed, 61 insertions, 25 deletions
diff --git a/lib/gitlab/background_migration/delete_diff_files.rb b/lib/gitlab/background_migration/delete_diff_files.rb
index 8fb2c334048..664ead1af44 100644
--- a/lib/gitlab/background_migration/delete_diff_files.rb
+++ b/lib/gitlab/background_migration/delete_diff_files.rb
@@ -4,41 +4,77 @@
 module Gitlab
   module BackgroundMigration
     class DeleteDiffFiles
-      def perform(merge_request_diff_id)
-        merge_request_diff = MergeRequestDiff.find_by(id: merge_request_diff_id)
+      class MergeRequestDiff < ActiveRecord::Base
+        self.table_name = 'merge_request_diffs'
 
-        return unless merge_request_diff
-        return unless should_delete_diff_files?(merge_request_diff)
+        belongs_to :merge_request
+        has_many :merge_request_diff_files
+      end
 
-        MergeRequestDiff.transaction do
-          merge_request_diff.update_column(:state, 'without_files')
-
-          # explain (analyze, buffers) when deleting 453 diff files:
-          #
-          # Delete on merge_request_diff_files  (cost=0.57..8487.35 rows=4846 width=6) (actual time=43.265..43.265 rows=0 loops=1)
-          #   Buffers: shared hit=2043 read=259 dirtied=254
-          #   ->  Index Scan using index_merge_request_diff_files_on_mr_diff_id_and_order on merge_request_diff_files  (cost=0.57..8487.35 rows=4846 width=6) (actu
-          # al time=0.466..26.317 rows=453 loops=1)
-          #         Index Cond: (merge_request_diff_id = 463448)
-          #         Buffers: shared hit=17 read=84
-          # Planning time: 0.107 ms
-          # Execution time: 43.287 ms
-          #
-          MergeRequestDiffFile.where(merge_request_diff_id: merge_request_diff.id).delete_all
+      class MergeRequestDiffFile < ActiveRecord::Base
+        self.table_name = 'merge_request_diff_files'
+      end
+
+      DEAD_TUPLES_THRESHOLD = 50_000
+      VACUUM_WAIT_TIME = 5.minutes
+
+      def perform(ids)
+        @ids = ids
+
+        # We should reschedule until deadtuples get in a desirable
+        # state (e.g. < 50_000). That may take more than one reschedule.
+        #
+        if should_wait_deadtuple_vacuum?
+          reschedule
+          return
         end
+
+        prune_diff_files
+      end
+
+      def should_wait_deadtuple_vacuum?
+        return false unless Gitlab::Database.postgresql?
+
+        diff_files_dead_tuples_count >= DEAD_TUPLES_THRESHOLD
       end
 
       private
 
-      def should_delete_diff_files?(merge_request_diff)
-        return false if merge_request_diff.state == 'without_files'
+      def reschedule
+        BackgroundMigrationWorker.perform_in(VACUUM_WAIT_TIME, self.class.name.demodulize, [@ids])
+      end
+
+      def diffs_collection
+        MergeRequestDiff.where(id: @ids)
+      end
+
+      def diff_files_dead_tuples_count
+        dead_tuple =
+          execute_statement("SELECT n_dead_tup FROM pg_stat_all_tables "\
+                            "WHERE relname = 'merge_request_diff_files'")[0]
 
-        merge_request = merge_request_diff.merge_request
+        dead_tuple&.fetch('n_dead_tup', 0).to_i
+      end
+
+      def prune_diff_files
+        removed = 0
+        updated = 0
 
-        return false unless merge_request.state == 'merged'
-        return false if merge_request_diff.id == merge_request.latest_merge_request_diff_id
+        MergeRequestDiff.transaction do
+          updated = diffs_collection.update_all(state: 'without_files')
+          removed = MergeRequestDiffFile.where(merge_request_diff_id: @ids).delete_all
+        end
+
+        log_info("Removed #{removed} merge_request_diff_files rows, "\
+                 "updated #{updated} merge_request_diffs rows")
+      end
+
+      def execute_statement(sql)
+        ActiveRecord::Base.connection.execute(sql)
+      end
 
-        true
+      def log_info(message)
+        Rails.logger.info("BackgroundMigration::DeleteDiffFiles - #{message}")
       end
     end
   end