Add Gitlab::Database::Subquery.self_join to delete_all with limit

`delete_all` doesn't support limit, so you'd need to subquery
that. And instead of subquerying with `where(id: query)`, it's better
to use an `INNER JOIN`. This method also works with MySQL, while
subquerying doesn't (without another layer of subquerying)

Reference:
https://stackoverflow.com/questions/17892762/mysql-this-version-of-mysql-doesnt-yet-support-limit-in-all-any-some-subqu/17892886#17892886

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/gitlab/database/subquery.rb b/lib/gitlab/database/subquery.rb
new file mode 100644
index 00000000000..2a6f39c6a27
--- /dev/null
+++ b/lib/gitlab/database/subquery.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Subquery
+      class << self
+        def self_join(relation)
+          t = relation.arel_table
+          t2 = relation.arel.as('t2')
+
+          relation.unscoped.joins(t.join(t2).on(t[:id].eq(t2[:id])).join_sources.first)
+        end
+      end
+    end
+  end
+end