perf(filter): Allow stale reads in filter

Allow reading from slave replicas when fetching all patterns for
patterns index.

cmd/checker/main.go

@@ -75,6 +75,7 @@ func main() {
 	defer telemetry.Stop()
 
 	databaseSettings := config.Redis.GetSettings()
+	databaseSettings.AllowSlaveReads = true
 	database := redis.NewDatabase(logger, databaseSettings, redis.Checker)
 
 	remoteConfig := config.Remote.GetRemoteSourceSettings()

filter/patterns_storage.go

@@ -30,7 +30,7 @@ func NewPatternStorage(database moira.Database, metrics *metrics.FilterMetrics,
 
 // Refresh builds pattern's indexes from redis data
 func (storage *PatternStorage) Refresh() error {
-	newPatterns, err := storage.database.GetPatterns()
+	newPatterns, err := storage.database.AllowStale().GetPatterns()
 	if err != nil {
 		return err
 	}

filter/patterns_storage_test.go

@@ -19,6 +19,7 @@ func TestProcessIncomingMetric(t *testing.T) {
 
 	mockCtrl := gomock.NewController(t)
 	database := mock_moira_alert.NewMockDatabase(mockCtrl)
+	database.EXPECT().AllowStale().AnyTimes().Return(database)
 	logger, _ := logging.GetLogger("Scheduler")
 
 	Convey("Create new pattern storage, GetPatterns returns error, should error", t, func() {

perfomance_tests/filter/filter_test.go

@@ -39,6 +39,7 @@ func BenchmarkProcessIncomingMetric(b *testing.B) {
 
 	mockCtrl := gomock.NewController(b)
 	database := mock_moira_alert.NewMockDatabase(mockCtrl)
+	database.EXPECT().AllowStale().AnyTimes().Return(database)
 	logger, _ := logging.GetLogger("Benchmark")
 
 	database.EXPECT().GetPatterns().Return(patterns, nil)