Metadata file indicating migration output version

Start with version 2, as the first version was implicit and did not use
a metadata file.

lib/gitlab/database/migrations/instrumentation.rb

@@ -17,7 +17,11 @@ module Gitlab
         def observe(version:, name:, connection:, &block)
           observation = Observation.new(version: version, name: name, success: false)
 
-          observers = observer_classes.map { |c| c.new(observation, @result_dir, connection) }
+          per_migration_result_dir = File.join(@result_dir, name)
+
+          FileUtils.mkdir_p(per_migration_result_dir)
+
+          observers = observer_classes.map { |c| c.new(observation, per_migration_result_dir, connection) }
 
           on_each_observer(observers) { |observer| observer.before }
 

lib/gitlab/database/migrations/observers/query_details.rb

@@ -6,7 +6,7 @@ module Gitlab
       module Observers
         class QueryDetails < MigrationObserver
           def before
-            file_path = File.join(output_dir, "#{observation.version}_#{observation.name}-query-details.json")
+            file_path = File.join(output_dir, "query-details.json")
             @file = File.open(file_path, 'wb')
             @writer = Oj::StreamWriter.new(@file, {})
             @writer.push_array

lib/gitlab/database/migrations/observers/query_log.rb

@@ -7,7 +7,7 @@ module Gitlab
         class QueryLog < MigrationObserver
           def before
             @logger_was = ActiveRecord::Base.logger
-            file_path = File.join(output_dir, "#{observation.version}_#{observation.name}.log")
+            file_path = File.join(output_dir, "migration.log")
             @logger = Logger.new(file_path)
             ActiveRecord::Base.logger = @logger
           end

lib/gitlab/database/migrations/observers/transaction_duration.rb

@@ -6,7 +6,7 @@ module Gitlab
       module Observers
         class TransactionDuration < MigrationObserver
           def before
-            file_path = File.join(output_dir, "#{observation.version}_#{observation.name}-transaction-duration.json")
+            file_path = File.join(output_dir, "transaction-duration.json")
             @file = File.open(file_path, 'wb')
             @writer = Oj::StreamWriter.new(@file, {})
             @writer.push_array

lib/gitlab/database/migrations/runner.rb

@@ -5,6 +5,8 @@ module Gitlab
     module Migrations
       class Runner
         BASE_RESULT_DIR = Rails.root.join('tmp', 'migration-testing').freeze
+        METADATA_FILENAME = 'metadata.json'
+        SCHEMA_VERSION = 2 # Version of the output format produced by the runner
 
         class << self
           def up
@@ -75,9 +77,11 @@ module Gitlab
           end
         ensure
           if instrumentation
-            File.open(File.join(result_dir, Gitlab::Database::Migrations::Instrumentation::STATS_FILENAME), 'wb+') do |io|
-              io << instrumentation.observations.to_json
-            end
+            stats_filename = File.join(result_dir, Gitlab::Database::Migrations::Instrumentation::STATS_FILENAME)
+            File.write(stats_filename, instrumentation.observations.to_json)
+
+            metadata_filename = File.join(result_dir, METADATA_FILENAME)
+            File.write(metadata_filename, { version: SCHEMA_VERSION }.to_json)
           end
 
           # We clear the cache here to mirror the cache clearing that happens at the end of `db:migrate` tasks

spec/lib/gitlab/database/migrations/observers/query_details_spec.rb

@@ -9,7 +9,7 @@ RSpec.describe Gitlab::Database::Migrations::Observers::QueryDetails do
   let(:query) { "select date_trunc('day', $1::timestamptz) + $2 * (interval '1 hour')" }
   let(:query_binds) { [Time.current, 3] }
   let(:directory_path) { Dir.mktmpdir }
-  let(:log_file) { "#{directory_path}/#{migration_version}_#{migration_name}-query-details.json" }
+  let(:log_file) { "#{directory_path}/query-details.json" }
   let(:query_details) { Gitlab::Json.parse(File.read(log_file)) }
   let(:migration_version) { 20210422152437 }
   let(:migration_name) { 'test' }

spec/lib/gitlab/database/migrations/observers/query_log_spec.rb

@@ -18,7 +18,7 @@ RSpec.describe Gitlab::Database::Migrations::Observers::QueryLog do
   it 'writes a file with the query log' do
     observe
 
-    expect(File.read("#{directory_path}/#{migration_version}_#{migration_name}.log")).to include(query)
+    expect(File.read("#{directory_path}/migration.log")).to include(query)
   end
 
   it 'does not change the default logger' do

spec/lib/gitlab/database/migrations/observers/transaction_duration_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe Gitlab::Database::Migrations::Observers::TransactionDuration do
   let(:connection) { ActiveRecord::Migration.connection }
   let(:observation) { Gitlab::Database::Migrations::Observation.new(version: migration_version, name: migration_name) }
   let(:directory_path) { Dir.mktmpdir }
-  let(:log_file) { "#{directory_path}/#{migration_version}_#{migration_name}-transaction-duration.json" }
+  let(:log_file) { "#{directory_path}/transaction-duration.json" }
   let(:transaction_duration) { Gitlab::Json.parse(File.read(log_file)) }
   let(:migration_version) { 20210422152437 }
   let(:migration_name) { 'test' }

spec/lib/gitlab/database/migrations/runner_spec.rb

@@ -79,6 +79,15 @@ RSpec.describe Gitlab::Database::Migrations::Runner do
         expect(migration_runs.map(&:dir)).to match_array([:up, :up])
         expect(migration_runs.map(&:version_to_migrate)).to eq(pending_migrations.map(&:version))
       end
+
+      it 'writes a metadata file with the current schema version' do
+        up.run
+
+        metadata_file = result_dir.join('up', described_class::METADATA_FILENAME)
+        expect(metadata_file.exist?).to be_truthy
+        metadata = Gitlab::Json.parse(File.read(metadata_file))
+        expect(metadata).to match('version' => described_class::SCHEMA_VERSION)
+      end
     end
   end
 
@@ -105,5 +114,14 @@ RSpec.describe Gitlab::Database::Migrations::Runner do
         expect(migration_runs.map(&:version_to_migrate)).to eq(applied_migrations_this_branch.reverse.map(&:version))
       end
     end
+
+    it 'writes a metadata file with the current schema version' do
+      down.run
+
+      metadata_file = result_dir.join('down', described_class::METADATA_FILENAME)
+      expect(metadata_file.exist?).to be_truthy
+      metadata = Gitlab::Json.parse(File.read(metadata_file))
+      expect(metadata).to match('version' => described_class::SCHEMA_VERSION)
+    end
   end
 end