Adds read-only mode for vmstorage node (#1680)

* adds read-only mode for vmstorage
https://github.com/VictoriaMetrics/VictoriaMetrics/issues/269

* changes order a bit

* moves isFreeDiskLimitReached var to storage struct
renames functions to be consistent
change protoparser api - with optional storage limit check for given openned storage

* renames freeSpaceLimit to ReadOnly

app/vmstorage/main.go

@@ -45,6 +45,9 @@ var (
 		"Excess series are logged and dropped. This can be useful for limiting series cardinality. See also -storage.maxDailySeries")
 	maxDailySeries = flag.Int("storage.maxDailySeries", 0, "The maximum number of unique series can be added to the storage during the last 24 hours. "+
 		"Excess series are logged and dropped. This can be useful for limiting series churn rate. See also -storage.maxHourlySeries")
+
+	minFreeDiskSpaceSizeBytes = flagutil.NewBytes("storage.minFreeDiskSpaceSize", 0, "Defines minimum free disk space size for storageDataPath. "+
+		"If limit is reached, storage becomes read-only and tells vminsert to reroute data for other storage nodes.")
 )
 
 // CheckTimeRange returns true if the given tr is denied for querying.
@@ -81,6 +84,7 @@ func InitWithoutMetrics(resetCacheIfNeeded func(mrs []storage.MetricRow)) {
 	storage.SetFinalMergeDelay(*finalMergeDelay)
 	storage.SetBigMergeWorkersCount(*bigMergeConcurrency)
 	storage.SetSmallMergeWorkersCount(*smallMergeConcurrency)
+	storage.SetFreeDiskSpaceLimit(minFreeDiskSpaceSizeBytes.N)
 
 	logger.Infof("opening storage at %q with -retentionPeriod=%s", *DataPath, retentionPeriod)
 	startTime := time.Now()
@@ -389,6 +393,17 @@ func registerStorageMetrics() {
 		return float64(fs.MustGetFreeSpace(*DataPath))
 	})
 
+	metrics.NewGauge(fmt.Sprintf(`vm_free_disk_space_limit_bytes{path=%q}`, *storageDataPath), func() float64 {
+		return float64(minFreeDiskSpaceSizeBytes.N)
+	})
+
+	metrics.NewGauge(`vm_storage_read_only`, func() float64 {
+		if strg.IsReadOnly() {
+			return 1
+		}
+		return 0
+	})
+
 	metrics.NewGauge(`vm_active_merges{type="storage/big"}`, func() float64 {
 		return float64(tm().ActiveBigMerges)
 	})

lib/storage/storage.go

@@ -57,6 +57,8 @@ type Storage struct {
 	hourlySeriesLimitRowsDropped uint64
 	dailySeriesLimitRowsDropped  uint64
 
+	isReadOnly uint32
+
 	path           string
 	cachePath      string
 	retentionMsecs int64
@@ -118,6 +120,7 @@ type Storage struct {
 	currHourMetricIDsUpdaterWG sync.WaitGroup
 	nextDayMetricIDsUpdaterWG  sync.WaitGroup
 	retentionWatcherWG         sync.WaitGroup
+	freeSpaceWatcherWG         sync.WaitGroup
 
 	// The snapshotLock prevents from concurrent creation of snapshots,
 	// since this may result in snapshots without recently added data,
@@ -258,6 +261,7 @@ func OpenStorage(path string, retentionMsecs int64, maxHourlySeries, maxDailySer
 	s.startCurrHourMetricIDsUpdater()
 	s.startNextDayMetricIDsUpdater()
 	s.startRetentionWatcher()
+	s.startFreeDiskSpaceWatcher()
 
 	return s, nil
 }
@@ -558,6 +562,53 @@ func (s *Storage) UpdateMetrics(m *Metrics) {
 	s.tb.UpdateMetrics(&m.TableMetrics)
 }
 
+var (
+	storageFreeSpaceLimitBytes uint64
+)
+
+// SetFreeDiskSpaceLimit sets the minimum free disk space size of current storage path
+//
+// The function must be called before opening or creating any storage.
+func SetFreeDiskSpaceLimit(bytes int) {
+	storageFreeSpaceLimitBytes = uint64(bytes)
+}
+
+// IsReadOnly returns information is storage in read only mode
+func (s *Storage) IsReadOnly() bool {
+	return atomic.LoadUint32(&s.isReadOnly) == 1
+}
+
+func (s *Storage) startFreeDiskSpaceWatcher() {
+	f := func() {
+		freeSpaceBytes := fs.MustGetFreeSpace(s.path)
+		// not enough free space
+		if freeSpaceBytes < storageFreeSpaceLimitBytes {
+			atomic.StoreUint32(&s.isReadOnly, 1)
+			return
+		}
+		atomic.StoreUint32(&s.isReadOnly, 0)
+	}
+	f()
+	s.freeSpaceWatcherWG.Add(1)
+	go func() {
+		defer s.freeSpaceWatcherWG.Done()
+		// zero value disables limit.
+		if storageFreeSpaceLimitBytes == 0 {
+			return
+		}
+		t := time.NewTicker(time.Minute)
+		defer t.Stop()
+		for {
+			select {
+			case <-s.stop:
+				return
+			case <-t.C:
+				f()
+			}
+		}
+	}()
+}
+
 func (s *Storage) startRetentionWatcher() {
 	s.retentionWatcherWG.Add(1)
 	go func() {
@@ -672,6 +723,7 @@ func (s *Storage) resetAndSaveTSIDCache() {
 func (s *Storage) MustClose() {
 	close(s.stop)
 
+	s.freeSpaceWatcherWG.Wait()
 	s.retentionWatcherWG.Wait()
 	s.currHourMetricIDsUpdaterWG.Wait()
 	s.nextDayMetricIDsUpdaterWG.Wait()