Remove subtransactions from partition management

lib/gitlab/database/partitioning/partition_manager.rb

@@ -74,8 +74,9 @@ module Gitlab
         end
 
         def create(partitions)
-          connection.transaction do
-            with_lock_retries do
+          # with_lock_retries starts a requires_new transaction most of the time, but not on the last iteration
+          with_lock_retries do
+            connection.transaction(requires_new: false) do # so we open a transaction here if not already in progress
               partitions.each do |partition|
                 connection.execute partition.to_sql
 
@@ -88,8 +89,9 @@ module Gitlab
         end
 
         def detach(partitions)
-          connection.transaction do
-            with_lock_retries do
+          # with_lock_retries starts a requires_new transaction most of the time, but not on the last iteration
+          with_lock_retries do
+            connection.transaction(requires_new: false) do # so we open a transaction here if not already in progress
               partitions.each { |p| detach_one_partition(p) }
             end
           end

spec/lib/gitlab/database/partitioning/partition_manager_spec.rb

@@ -18,6 +18,11 @@ RSpec.describe Gitlab::Database::Partitioning::PartitionManager do
     it 'remembers registered models' do
       expect { described_class.register(model) }.to change { described_class.models }.to include(model)
     end
+
+    after do
+      # Do not leak the double to other specs
+      described_class.models.delete(model)
+    end
   end
 
   context 'creating partitions (mocked)' do