Fix excessive logging by instrumentation plugin

lib/rom/plugins/relation/sql/instrumentation.rb

@@ -35,6 +35,8 @@ module Instrumentation
             db_notifications = relations.values.map { |r| [r.dataset.db, r.notifications] }.uniq.to_h
 
             db_notifications.each do |db, notifications|
+              next if db.respond_to?(:rom_instrumentation?)
+
               instrumenter = Instrumenter.new(db.database_type, notifications)
               db.extend(instrumenter)
             end
@@ -56,6 +58,8 @@ class Instrumenter < Module
 
             # @api private
             def initialize(name, notifications)
+              super()
+
               @name = name
               @notifications = notifications
               define_log_connection_yield
@@ -68,6 +72,8 @@ def define_log_connection_yield
               name = self.name
               notifications = self.notifications
 
+              define_method(:rom_instrumentation?) { true }
+
               define_method(:log_connection_yield) do |*args, &block|
                 notifications.instrument(:sql, name: name, query: args[0]) do
                   super(*args, &block)

spec/unit/relation/instrument_spec.rb

@@ -64,4 +64,30 @@ def instrument(*args, &block)
     expect(notifications.logs).
       to include([:sql, name: :sqlite, query: "SELECT count(*) AS 'count' FROM `users` LIMIT 1"])
   end
+
+  context 'two containers with shared gateway' do
+    let(:conf_alt) { TestConfiguration.new(:sql, conn) }
+
+    let(:container_alt) { ROM.container(conf_alt) }
+
+    before do
+      conf_alt.plugin(:sql, relations: :instrumentation)
+
+      conf_alt.relation(:users) do
+        schema(infer: true)
+      end
+
+      container_alt
+    end
+
+    it 'instruments relation materialization but does it once' do
+      relation.to_a
+
+      entries = notifications.logs.count do |log|
+        log.eql?([:sql, name: :sqlite, query: relation.dataset.sql])
+      end
+
+      expect(entries).to be(1)
+    end
+  end
 end