3 files changed, 34 insertions, 3 deletions
diff --git a/lib/gitlab/database/migrations/instrumentation.rb b/lib/gitlab/database/migrations/instrumentation.rb
index 959028ce00b..e9ef80d5198 100644
--- a/lib/gitlab/database/migrations/instrumentation.rb
+++ b/lib/gitlab/database/migrations/instrumentation.rb
@@ -4,6 +4,9 @@ module Gitlab
   module Database
     module Migrations
       class Instrumentation
+        RESULT_DIR = Rails.root.join('tmp', 'migration-testing').freeze
+        STATS_FILENAME = 'migration-stats.json'
+
         attr_reader :observations
 
         def initialize(observers = ::Gitlab::Database::Migrations::Observers.all_observers)
@@ -21,7 +24,7 @@ module Gitlab
 
           observation.walltime = Benchmark.realtime do
             yield
-          rescue => e
+          rescue StandardError => e
             exception = e
             observation.success = false
           end
@@ -47,7 +50,7 @@ module Gitlab
         def on_each_observer(&block)
           observers.each do |observer|
             yield observer
-          rescue => e
+          rescue StandardError => e
             Gitlab::AppLogger.error("Migration observer #{observer.class} failed with: #{e}")
           end
         end
diff --git a/lib/gitlab/database/migrations/observers.rb b/lib/gitlab/database/migrations/observers.rb
index 592993aeac5..b65a303ef30 100644
--- a/lib/gitlab/database/migrations/observers.rb
+++ b/lib/gitlab/database/migrations/observers.rb
@@ -7,7 +7,8 @@ module Gitlab
         def self.all_observers
           [
             TotalDatabaseSizeChange.new,
-            QueryStatistics.new
+            QueryStatistics.new,
+            QueryLog.new
           ]
         end
       end
diff --git a/lib/gitlab/database/migrations/observers/query_log.rb b/lib/gitlab/database/migrations/observers/query_log.rb
new file mode 100644
index 00000000000..45df07fe391
--- /dev/null
+++ b/lib/gitlab/database/migrations/observers/query_log.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Migrations
+      module Observers
+        class QueryLog < MigrationObserver
+          def before
+            @logger_was = ActiveRecord::Base.logger
+            @log_file_path = File.join(Instrumentation::RESULT_DIR, 'current.log')
+            @logger = Logger.new(@log_file_path)
+            ActiveRecord::Base.logger = @logger
+          end
+
+          def after
+            ActiveRecord::Base.logger = @logger_was
+            @logger.close
+          end
+
+          def record(observation)
+            File.rename(@log_file_path, File.join(Instrumentation::RESULT_DIR, "#{observation.migration}.log"))
+          end
+        end
+      end
+    end
+  end
+end