Simplify migration observers

They do not need to rename the file anymore since they are
instantiated with information about the migration being observed.

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

@@ -6,8 +6,8 @@ module Gitlab
       module Observers
         class QueryDetails < MigrationObserver
           def before
-            @file_path = File.join(Instrumentation::RESULT_DIR, 'current-details.json')
-            @file = File.open(@file_path, 'wb')
+            file_path = File.join(Instrumentation::RESULT_DIR, "#{observation.version}_#{observation.name}-query-details.json")
+            @file = File.open(file_path, 'wb')
             @writer = Oj::StreamWriter.new(@file, {})
             @writer.push_array
             @subscriber = ActiveSupport::Notifications.subscribe('sql.active_record') do |*args|
@@ -23,7 +23,7 @@ module Gitlab
           end
 
           def record
-            File.rename(@file_path, File.join(Instrumentation::RESULT_DIR, "#{observation.version}_#{observation.name}-query-details.json"))
+            # no-op
           end
 
           def record_sql_event(_name, started, finished, _unique_id, payload)

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

@@ -7,8 +7,8 @@ module Gitlab
         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)
+            file_path = File.join(Instrumentation::RESULT_DIR, "#{observation.version}_#{observation.name}.log")
+            @logger = Logger.new(file_path)
             ActiveRecord::Base.logger = @logger
           end
 
@@ -18,7 +18,7 @@ module Gitlab
           end
 
           def record
-            File.rename(@log_file_path, File.join(Instrumentation::RESULT_DIR, "#{observation.version}_#{observation.name}.log"))
+            # no-op
           end
         end
       end

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

@@ -8,7 +8,6 @@ RSpec.describe Gitlab::Database::Migrations::Observers::QueryLog do
   let(:connection) { ActiveRecord::Base.connection }
   let(:query) { 'select 1' }
   let(:directory_path) { Dir.mktmpdir }
-  let(:log_file) { "#{directory_path}/current.log" }
   let(:migration_version) { 20210422152437 }
   let(:migration_name) { 'test' }