Temporary instrumention for internal id lock

This adds a temporary counter `gitlab_internal_id_for_update_lock`
tracking the number of `ROW SHARE` locks on internal id records.

The counter has an additional dimension `usage` which indicates
what kind of internal id lock scope was used. Also, `changed` indicates
whether or not the actual counter value changed with the attempted
update.

This is a preparation for
https://gitlab.com/gitlab-org/gitlab/issues/30515

app/models/internal_id.rb

@@ -16,6 +16,8 @@
 # * Add `usage` value to enum
 # * (Optionally) add columns to `internal_ids` if needed for scope.
 class InternalId < ApplicationRecord
+  include Gitlab::Utils::StrongMemoize
+
   belongs_to :project
   belongs_to :namespace
 
@@ -47,10 +49,18 @@ class InternalId < ApplicationRecord
   def update_and_save(&block)
     lock!
     yield
+    update_and_save_counter.increment(usage: usage, changed: last_value_changed?)
     save!
     last_value
   end
 
+  # Temporary instrumentation to track for-update locks
+  def update_and_save_counter
+    strong_memoize(:update_and_save_counter) do
+      Gitlab::Metrics.counter(:gitlab_internal_id_for_update_lock, 'Number of ROW SHARE (FOR UPDATE) locks on individual records from internal_ids')
+    end
+  end
+
   class << self
     def track_greatest(subject, scope, usage, new_value, init)
       return new_value unless available?

spec/services/ci/create_pipeline_service_spec.rb

@@ -71,6 +71,7 @@ describe Ci::CreatePipelineService do
         expect(Gitlab::Metrics).to receive(:counter)
           .with(:pipelines_created_total, "Counter of pipelines created")
           .and_call_original
+        allow(Gitlab::Metrics).to receive(:counter).and_call_original # allow other counters
 
         pipeline
       end