Ignore irrelevant sql commands in metrics

Fix #51005

changelogs/unreleased/skip-irrelevant-sql-commands-in-metrics.yml

+---
+title: Ignore irrelevant sql commands in metrics
+merge_request: 21498
+author:
+type: other

lib/gitlab/metrics/subscribers/active_record.rb

@@ -6,9 +6,15 @@ module Gitlab
         include Gitlab::Metrics::Methods
         attach_to :active_record
 
+        IGNORABLE_SQL = %w{BEGIN COMMIT}.freeze
+
         def sql(event)
           return unless current_transaction
 
+          payload = event.payload
+
+          return if payload[:name] == 'SCHEMA' || IGNORABLE_SQL.include?(payload[:sql])
+
           self.class.gitlab_sql_duration_seconds.observe(current_transaction.labels, event.duration / 1000.0)
 
           current_transaction.increment(:sql_duration, event.duration, false)

spec/lib/gitlab/metrics/subscribers/active_record_spec.rb

@@ -42,6 +42,65 @@ describe Gitlab::Metrics::Subscribers::ActiveRecord do
 
         subscriber.sql(event)
       end
+
+      context 'events are internal to Rails or irrelevant' do
+        let(:schema_event) do
+          double(
+            :event,
+            name: 'sql.active_record',
+            payload: {
+              sql: "SELECT attr.attname FROM pg_attribute attr INNER JOIN pg_constraint cons ON attr.attrelid = cons.conrelid AND attr.attnum = any(cons.conkey) WHERE cons.contype = 'p' AND cons.conrelid = '\"projects\"'::regclass",
+              name: 'SCHEMA',
+              connection_id: 135,
+              statement_name: nil,
+              binds: []
+            },
+            duration: 0.7
+          )
+        end
+
+        let(:begin_event) do
+          double(
+            :event,
+            name: 'sql.active_record',
+            payload: {
+              sql: "BEGIN",
+              name: nil,
+              connection_id: 231,
+              statement_name: nil,
+              binds: []
+            },
+            duration: 1.1
+          )
+        end
+
+        let(:commit_event) do
+          double(
+            :event,
+            name: 'sql.active_record',
+            payload: {
+              sql: "COMMIT",
+              name: nil,
+              connection_id: 212,
+              statement_name: nil,
+              binds: []
+            },
+            duration: 1.6
+          )
+        end
+
+        it 'skips schema/begin/commit sql commands' do
+          expect(subscriber).to receive(:current_transaction)
+                                  .at_least(:once)
+                                  .and_return(transaction)
+
+          expect(transaction).not_to receive(:increment)
+
+          subscriber.sql(schema_event)
+          subscriber.sql(begin_event)
+          subscriber.sql(commit_event)
+        end
+      end
     end
   end
 end