lib/storage: return back inmemory inverted index for recent hour

Issues fixed:
- Slow startup times. Now the index is loaded from cache during start.
- High memory usage related to superflouos index copies every 10 seconds.

app/vmstorage/main.go

@@ -407,6 +407,25 @@ func registerStorageMetrics() {
 		return float64(idbm().ItemsCount)
 	})
 
+	metrics.NewGauge(`vm_recent_hour_inverted_index_entries`, func() float64 {
+		return float64(m().RecentHourInvertedIndexSize)
+	})
+	metrics.NewGauge(`vm_recent_hour_inverted_index_size_bytes`, func() float64 {
+		return float64(m().RecentHourInvertedIndexSizeBytes)
+	})
+	metrics.NewGauge(`vm_recent_hour_inverted_index_unique_tag_pairs`, func() float64 {
+		return float64(m().RecentHourInvertedIndexUniqueTagPairsSize)
+	})
+	metrics.NewGauge(`vm_recent_hour_inverted_index_pending_metric_ids`, func() float64 {
+		return float64(m().RecentHourInvertedIndexPendingMetricIDsSize)
+	})
+	metrics.NewGauge(`vm_recent_hour_inverted_index_search_calls_total`, func() float64 {
+		return float64(idbm().RecentHourInvertedIndexSearchCalls)
+	})
+	metrics.NewGauge(`vm_recent_hour_inverted_index_search_hits_total`, func() float64 {
+		return float64(idbm().RecentHourInvertedIndexSearchHits)
+	})
+
 	metrics.NewGauge(`vm_date_range_search_calls_total`, func() float64 {
 		return float64(idbm().DateRangeSearchCalls)
 	})

lib/storage/index_db.go

@@ -95,6 +95,12 @@ type indexDB struct {
 	// The number of successful searches for metric ids by days.
 	dateMetricIDsSearchHits uint64
 
+	// The number of calls for recent hour searches over inverted index.
+	recentHourInvertedIndexSearchCalls uint64
+
+	// The number of hits for recent hour searches over inverted index.
+	recentHourInvertedIndexSearchHits uint64
+
 	// The number of calls for date range searches.
 	dateRangeSearchCalls uint64
 
@@ -225,6 +231,9 @@ type IndexDBMetrics struct {
 	DateMetricIDsSearchCalls       uint64
 	DateMetricIDsSearchHits        uint64
 
+	RecentHourInvertedIndexSearchCalls uint64
+	RecentHourInvertedIndexSearchHits  uint64
+
 	DateRangeSearchCalls uint64
 	DateRangeSearchHits  uint64
 
@@ -266,6 +275,9 @@ func (db *indexDB) UpdateMetrics(m *IndexDBMetrics) {
 	m.DateMetricIDsSearchCalls += atomic.LoadUint64(&db.dateMetricIDsSearchCalls)
 	m.DateMetricIDsSearchHits += atomic.LoadUint64(&db.dateMetricIDsSearchHits)
 
+	m.RecentHourInvertedIndexSearchCalls += atomic.LoadUint64(&db.recentHourInvertedIndexSearchCalls)
+	m.RecentHourInvertedIndexSearchHits += atomic.LoadUint64(&db.recentHourInvertedIndexSearchHits)
+
 	m.DateRangeSearchCalls += atomic.LoadUint64(&db.dateRangeSearchCalls)
 	m.DateRangeSearchHits += atomic.LoadUint64(&db.dateRangeSearchHits)
 
@@ -1655,6 +1667,10 @@ func (is *indexSearch) updateMetricIDsForTagFilters(metricIDs *uint64set.Set, tf
 		return bytes.Compare(a.prefix, b.prefix) < 0
 	})
 
+	if is.tryUpdatingMetricIDsForRecentHour(metricIDs, tfs, tr) {
+		// Fast path: found metricIDs in the inmemoryInvertedIndex for the last hour.
+		return nil
+	}
 	ok, err := is.tryUpdatingMetricIDsForDateRange(metricIDs, tfs, tr, maxMetrics)
 	if err != nil {
 		return err
@@ -2177,6 +2193,34 @@ func (is *indexSearch) getMetricIDsForRecentHours(tr TimeRange, maxMetrics int)
 	return nil, false
 }
 
+func (is *indexSearch) tryUpdatingMetricIDsForRecentHour(metricIDs *uint64set.Set, tfs *TagFilters, tr TimeRange) bool {
+	minHour := uint64(tr.MinTimestamp) / msecPerHour
+	maxHour := uint64(tr.MaxTimestamp) / msecPerHour
+
+	hmCurr := is.db.currHourMetricIDs.Load().(*hourMetricIDs)
+	if maxHour == hmCurr.hour && minHour == maxHour && hmCurr.isFull {
+		// The tr fits the current hour.
+		hmCurr.iidx.UpdateMetricIDsForTagFilters(metricIDs, hmCurr.m, tfs)
+		atomic.AddUint64(&is.db.recentHourInvertedIndexSearchHits, 1)
+		return true
+	}
+	hmPrev := is.db.prevHourMetricIDs.Load().(*hourMetricIDs)
+	if maxHour == hmPrev.hour && minHour == maxHour && hmPrev.isFull {
+		// The tr fits the previous hour.
+		hmPrev.iidx.UpdateMetricIDsForTagFilters(metricIDs, hmPrev.m, tfs)
+		atomic.AddUint64(&is.db.recentHourInvertedIndexSearchHits, 1)
+		return true
+	}
+	if maxHour == hmCurr.hour && minHour == hmPrev.hour && hmCurr.isFull && hmPrev.isFull {
+		// The tr spans the previous and the current hours.
+		hmPrev.iidx.UpdateMetricIDsForTagFilters(metricIDs, hmPrev.m, tfs)
+		hmCurr.iidx.UpdateMetricIDsForTagFilters(metricIDs, hmCurr.m, tfs)
+		atomic.AddUint64(&is.db.recentHourInvertedIndexSearchHits, 1)
+		return true
+	}
+	return false
+}
+
 func (db *indexDB) storeDateMetricID(date, metricID uint64) error {
 	is := db.getIndexSearch()
 	ok, err := is.hasDateMetricID(date, metricID)

lib/storage/index_db_test.go

@@ -1418,6 +1418,10 @@ func TestSearchTSIDWithTimeRange(t *testing.T) {
 				prevMetricIDs.m.Add(tsids[i].MetricID)
 				currMetricIDs.m.Add(tsids[i].MetricID)
 			}
+			prevMetricIDs.iidx = newInmemoryInvertedIndex()
+			prevMetricIDs.iidx.MustUpdate(db, prevMetricIDs.m)
+			currMetricIDs.iidx = newInmemoryInvertedIndex()
+			currMetricIDs.iidx.MustUpdate(db, currMetricIDs.m)
 		}
 	}
 

lib/storage/inmemory_inverted_index.go

@@ -0,0 +1,283 @@
+package storage
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"sync"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/uint64set"
+)
+
+type inmemoryInvertedIndex struct {
+	mu               sync.RWMutex
+	m                map[string]*uint64set.Set
+	pendingMetricIDs []uint64
+}
+
+func (iidx *inmemoryInvertedIndex) Marshal(dst []byte) []byte {
+	iidx.mu.RLock()
+	defer iidx.mu.RUnlock()
+
+	// Marshal iidx.m
+	var metricIDs []uint64
+	dst = encoding.MarshalUint64(dst, uint64(len(iidx.m)))
+	for k, v := range iidx.m {
+		dst = encoding.MarshalBytes(dst, []byte(k))
+		metricIDs = v.AppendTo(metricIDs[:0])
+		dst = marshalMetricIDs(dst, metricIDs)
+	}
+
+	// Marshal iidx.pendingMetricIDs
+	dst = marshalMetricIDs(dst, iidx.pendingMetricIDs)
+
+	return dst
+}
+
+func (iidx *inmemoryInvertedIndex) Unmarshal(src []byte) ([]byte, error) {
+	iidx.mu.Lock()
+	defer iidx.mu.Unlock()
+
+	// Unmarshal iidx.m
+	if len(src) < 8 {
+		return src, fmt.Errorf("cannot read len(iidx.m) from %d bytes; want at least 8 bytes", len(src))
+	}
+	mLen := int(encoding.UnmarshalUint64(src))
+	src = src[8:]
+	m := make(map[string]*uint64set.Set, mLen)
+	var metricIDs []uint64
+	for i := 0; i < mLen; i++ {
+		tail, k, err := encoding.UnmarshalBytes(src)
+		if err != nil {
+			return tail, fmt.Errorf("cannot unmarshal key #%d for iidx.m: %s", i, err)
+		}
+		src = tail
+		tail, metricIDs, err = unmarshalMetricIDs(metricIDs[:0], src)
+		if err != nil {
+			return tail, fmt.Errorf("cannot unmarshal value #%d for iidx.m: %s", i, err)
+		}
+		src = tail
+		var v uint64set.Set
+		for _, metricID := range metricIDs {
+			v.Add(metricID)
+		}
+		m[string(k)] = &v
+	}
+	iidx.m = m
+
+	// Unmarshal iidx.pendingMetricIDs
+	var err error
+	var tail []byte
+	tail, metricIDs, err = unmarshalMetricIDs(metricIDs[:0], src)
+	if err != nil {
+		return tail, fmt.Errorf("cannot unmarshal iidx.pendingMetricIDs: %s", err)
+	}
+	src = tail
+	iidx.pendingMetricIDs = append(iidx.pendingMetricIDs[:0], metricIDs...)
+
+	return src, nil
+}
+
+func marshalMetricIDs(dst []byte, metricIDs []uint64) []byte {
+	dst = encoding.MarshalUint64(dst, uint64(len(metricIDs)))
+	for _, metricID := range metricIDs {
+		dst = encoding.MarshalUint64(dst, metricID)
+	}
+	return dst
+}
+
+func unmarshalMetricIDs(dst []uint64, src []byte) ([]byte, []uint64, error) {
+	if len(src) < 8 {
+		return src, dst, fmt.Errorf("cannot unmarshal metricIDs len from %d bytes; want at least 8 bytes", len(src))
+	}
+	metricIDsLen := int(encoding.UnmarshalUint64(src))
+	src = src[8:]
+	if len(src) < 8*metricIDsLen {
+		return src, dst, fmt.Errorf("not enough bytes for unmarshaling %d metricIDs; want %d bytes; got %d bytes", metricIDsLen, 8*metricIDsLen, len(src))
+	}
+	for i := 0; i < metricIDsLen; i++ {
+		metricID := encoding.UnmarshalUint64(src)
+		src = src[8:]
+		dst = append(dst, metricID)
+	}
+	return src, dst, nil
+}
+
+func (iidx *inmemoryInvertedIndex) SizeBytes() uint64 {
+	n := uint64(0)
+	iidx.mu.RLock()
+	for k, v := range iidx.m {
+		n += uint64(len(k))
+		n += v.SizeBytes()
+	}
+	n += uint64(len(iidx.pendingMetricIDs)) * 8
+	iidx.mu.RUnlock()
+	return n
+}
+
+func (iidx *inmemoryInvertedIndex) GetUniqueTagPairsLen() int {
+	if iidx == nil {
+		return 0
+	}
+	iidx.mu.RLock()
+	n := len(iidx.m)
+	iidx.mu.RUnlock()
+	return n
+}
+
+func (iidx *inmemoryInvertedIndex) GetEntriesCount() int {
+	if iidx == nil {
+		return 0
+	}
+	n := 0
+	iidx.mu.RLock()
+	for _, v := range iidx.m {
+		n += v.Len()
+	}
+	iidx.mu.RUnlock()
+	return n
+}
+
+func (iidx *inmemoryInvertedIndex) GetPendingMetricIDsLen() int {
+	if iidx == nil {
+		return 0
+	}
+	iidx.mu.RLock()
+	n := len(iidx.pendingMetricIDs)
+	iidx.mu.RUnlock()
+	return n
+}
+
+func newInmemoryInvertedIndex() *inmemoryInvertedIndex {
+	return &inmemoryInvertedIndex{
+		m: make(map[string]*uint64set.Set),
+	}
+}
+
+func (iidx *inmemoryInvertedIndex) MustUpdate(idb *indexDB, src *uint64set.Set) {
+	metricIDs := src.AppendTo(nil)
+	iidx.mu.Lock()
+	iidx.pendingMetricIDs = append(iidx.pendingMetricIDs, metricIDs...)
+	if err := iidx.addPendingEntriesLocked(idb); err != nil {
+		logger.Panicf("FATAL: cannot update inmemoryInvertedIndex with pendingMetricIDs: %s", err)
+	}
+	iidx.mu.Unlock()
+}
+
+func (iidx *inmemoryInvertedIndex) AddMetricID(idb *indexDB, metricID uint64) {
+	iidx.mu.Lock()
+	iidx.pendingMetricIDs = append(iidx.pendingMetricIDs, metricID)
+	if err := iidx.addPendingEntriesLocked(idb); err != nil {
+		logger.Panicf("FATAL: cannot update inmemoryInvertedIndex with pendingMetricIDs: %s", err)
+	}
+	iidx.mu.Unlock()
+}
+
+func (iidx *inmemoryInvertedIndex) UpdateMetricIDsForTagFilters(metricIDs, allMetricIDs *uint64set.Set, tfs *TagFilters) {
+	if iidx == nil {
+		return
+	}
+	var result *uint64set.Set
+	var tfFirst *tagFilter
+	for i := range tfs.tfs {
+		if tfs.tfs[i].isNegative {
+			continue
+		}
+		tfFirst = &tfs.tfs[i]
+		break
+	}
+
+	iidx.mu.RLock()
+	defer iidx.mu.RUnlock()
+
+	if tfFirst == nil {
+		result = allMetricIDs.Clone()
+	} else {
+		result = iidx.getMetricIDsForTagFilterLocked(tfFirst, tfs.commonPrefix)
+	}
+	for i := range tfs.tfs {
+		tf := &tfs.tfs[i]
+		if tf == tfFirst {
+			continue
+		}
+		m := iidx.getMetricIDsForTagFilterLocked(tf, tfs.commonPrefix)
+		if tf.isNegative {
+			result.Subtract(m)
+		} else {
+			result.Intersect(m)
+		}
+		if result.Len() == 0 {
+			return
+		}
+	}
+	metricIDs.Union(result)
+}
+
+func (iidx *inmemoryInvertedIndex) getMetricIDsForTagFilterLocked(tf *tagFilter, commonPrefix []byte) *uint64set.Set {
+	if !bytes.HasPrefix(tf.prefix, commonPrefix) {
+		logger.Panicf("BUG: tf.prefix must start with commonPrefix=%q; got %q", commonPrefix, tf.prefix)
+	}
+	prefix := tf.prefix[len(commonPrefix):]
+	var m uint64set.Set
+	kb := kbPool.Get()
+	defer kbPool.Put(kb)
+	for k, v := range iidx.m {
+		if len(k) < len(prefix) || k[:len(prefix)] != string(prefix) {
+			continue
+		}
+		kb.B = append(kb.B[:0], k[len(prefix):]...)
+		ok, err := tf.matchSuffix(kb.B)
+		if err != nil {
+			logger.Panicf("BUG: unexpected error from matchSuffix(%q): %s", kb.B, err)
+		}
+		if !ok {
+			continue
+		}
+		m.Union(v)
+	}
+	return &m
+}
+
+func (iidx *inmemoryInvertedIndex) addPendingEntriesLocked(idb *indexDB) error {
+	metricIDs := iidx.pendingMetricIDs
+	iidx.pendingMetricIDs = iidx.pendingMetricIDs[:0]
+
+	kb := kbPool.Get()
+	defer kbPool.Put(kb)
+
+	mn := GetMetricName()
+	defer PutMetricName(mn)
+	for _, metricID := range metricIDs {
+		var err error
+		kb.B, err = idb.searchMetricName(kb.B[:0], metricID)
+		if err != nil {
+			if err == io.EOF {
+				iidx.pendingMetricIDs = append(iidx.pendingMetricIDs, metricID)
+				continue
+			}
+			return fmt.Errorf("cannot find metricName by metricID %d: %s", metricID, err)
+		}
+		if err = mn.Unmarshal(kb.B); err != nil {
+			return fmt.Errorf("cannot unmarshal metricName %q: %s", kb.B, err)
+		}
+		kb.B = marshalTagValue(kb.B[:0], nil)
+		kb.B = marshalTagValue(kb.B, mn.MetricGroup)
+		iidx.addMetricIDLocked(kb.B, metricID)
+		for i := range mn.Tags {
+			kb.B = mn.Tags[i].Marshal(kb.B[:0])
+			iidx.addMetricIDLocked(kb.B, metricID)
+		}
+	}
+	return nil
+}
+
+func (iidx *inmemoryInvertedIndex) addMetricIDLocked(key []byte, metricID uint64) {
+	v := iidx.m[string(key)]
+	if v == nil {
+		v = &uint64set.Set{}
+		iidx.m[string(key)] = v
+	}
+	v.Add(metricID)
+}

lib/storage/inmemory_inverted_index_test.go

@@ -0,0 +1,40 @@
+package storage
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+func TestInmemoryInvertedIndexMarshalUnmarshal(t *testing.T) {
+	iidx := newInmemoryInvertedIndex()
+	const keysCount = 100
+	const metricIDsCount = 10000
+	for i := 0; i < metricIDsCount; i++ {
+		k := fmt.Sprintf("key %d", i%keysCount)
+		iidx.addMetricIDLocked([]byte(k), uint64(i))
+	}
+
+	data := iidx.Marshal(nil)
+
+	iidx2 := newInmemoryInvertedIndex()
+	tail, err := iidx2.Unmarshal(data)
+	if err != nil {
+		t.Fatalf("cannot unmarshal iidx: %s", err)
+	}
+	if len(tail) != 0 {
+		t.Fatalf("unexpected tail left after iidx unmarshaling: %d bytes", len(tail))
+	}
+	if len(iidx.m) != len(iidx2.m) {
+		t.Fatalf("unexpected len(iidx2.m); got %d; want %d", len(iidx2.m), len(iidx.m))
+	}
+	if !reflect.DeepEqual(iidx.pendingMetricIDs, iidx2.pendingMetricIDs) {
+		t.Fatalf("unexpected pendingMetricIDs; got\n%d;\nwant\n%d", iidx2.pendingMetricIDs, iidx.pendingMetricIDs)
+	}
+	for k, v := range iidx.m {
+		v2 := iidx2.m[k]
+		if !v.Equal(v2) {
+			t.Fatalf("unexpected set for key %q", k)
+		}
+	}
+}

lib/storage/search_test.go

@@ -72,15 +72,21 @@ func TestSearchQueryMarshalUnmarshal(t *testing.T) {
 
 func TestSearch(t *testing.T) {
 	t.Run("global_inverted_index", func(t *testing.T) {
-		testSearchGeneric(t, false)
+		testSearchGeneric(t, false, false)
 	})
 	t.Run("perday_inverted_index", func(t *testing.T) {
-		testSearchGeneric(t, true)
+		testSearchGeneric(t, false, true)
+	})
+	t.Run("recent_hour_global_inverted_index", func(t *testing.T) {
+		testSearchGeneric(t, true, false)
+	})
+	t.Run("recent_hour_perday_inverted_index", func(t *testing.T) {
+		testSearchGeneric(t, true, true)
 	})
 }
 
-func testSearchGeneric(t *testing.T, forcePerDayInvertedIndex bool) {
-	path := fmt.Sprintf("TestSearch_%v", forcePerDayInvertedIndex)
+func testSearchGeneric(t *testing.T, forceRecentHourInvertedIndex, forcePerDayInvertedIndex bool) {
+	path := fmt.Sprintf("TestSearch_%v_%v", forceRecentHourInvertedIndex, forcePerDayInvertedIndex)
 	st, err := OpenStorage(path, 0)
 	if err != nil {
 		t.Fatalf("cannot open storage %q: %s", path, err)
@@ -141,6 +147,10 @@ func testSearchGeneric(t *testing.T, forcePerDayInvertedIndex bool) {
 			extDB.startDateForPerDayInvertedIndex = 0
 		})
 	}
+	if forceRecentHourInvertedIndex {
+		hm := st.currHourMetricIDs.Load().(*hourMetricIDs)
+		hm.isFull = true
+	}
 
 	// Run search.
 	tr := TimeRange{

lib/storage/storage.go

@@ -311,6 +311,11 @@ type Metrics struct {
 
 	HourMetricIDCacheSize uint64
 
+	RecentHourInvertedIndexSize                 uint64
+	RecentHourInvertedIndexSizeBytes            uint64
+	RecentHourInvertedIndexUniqueTagPairsSize   uint64
+	RecentHourInvertedIndexPendingMetricIDsSize uint64
+
 	IndexDBMetrics IndexDBMetrics
 	TableMetrics   TableMetrics
 }
@@ -367,6 +372,18 @@ func (s *Storage) UpdateMetrics(m *Metrics) {
 	}
 	m.HourMetricIDCacheSize += uint64(hourMetricIDsLen)
 
+	m.RecentHourInvertedIndexSize += uint64(hmPrev.iidx.GetEntriesCount())
+	m.RecentHourInvertedIndexSize += uint64(hmCurr.iidx.GetEntriesCount())
+
+	m.RecentHourInvertedIndexSizeBytes += hmPrev.iidx.SizeBytes()
+	m.RecentHourInvertedIndexSizeBytes += hmCurr.iidx.SizeBytes()
+
+	m.RecentHourInvertedIndexUniqueTagPairsSize += uint64(hmPrev.iidx.GetUniqueTagPairsLen())
+	m.RecentHourInvertedIndexUniqueTagPairsSize += uint64(hmCurr.iidx.GetUniqueTagPairsLen())
+
+	m.RecentHourInvertedIndexPendingMetricIDsSize += uint64(hmPrev.iidx.GetPendingMetricIDsLen())
+	m.RecentHourInvertedIndexPendingMetricIDsSize += uint64(hmCurr.iidx.GetPendingMetricIDsLen())
+
 	s.idb().UpdateMetrics(&m.IndexDBMetrics)
 	s.tb.UpdateMetrics(&m.TableMetrics)
 }
@@ -481,6 +498,7 @@ func (s *Storage) mustLoadHourMetricIDs(hour uint64, name string) *hourMetricIDs
 	if !fs.IsPathExist(path) {
 		logger.Infof("nothing to load from %q", path)
 		return &hourMetricIDs{
+			iidx: newInmemoryInvertedIndex(),
 			hour: hour,
 		}
 	}
@@ -492,6 +510,7 @@ func (s *Storage) mustLoadHourMetricIDs(hour uint64, name string) *hourMetricIDs
 	if len(src) < 24 {
 		logger.Errorf("discarding %s, since it has broken header; got %d bytes; want %d bytes", path, len(src), 24)
 		return &hourMetricIDs{
+			iidx: newInmemoryInvertedIndex(),
 			hour: hour,
 		}
 	}
@@ -504,6 +523,7 @@ func (s *Storage) mustLoadHourMetricIDs(hour uint64, name string) *hourMetricIDs
 	if hourLoaded != hour {
 		logger.Infof("discarding %s, since it contains outdated hour; got %d; want %d", name, hourLoaded, hour)
 		return &hourMetricIDs{
+			iidx: newInmemoryInvertedIndex(),
 			hour: hour,
 		}
 	}
@@ -511,9 +531,10 @@ func (s *Storage) mustLoadHourMetricIDs(hour uint64, name string) *hourMetricIDs
 	// Unmarshal hm.m
 	hmLen := encoding.UnmarshalUint64(src)
 	src = src[8:]
-	if uint64(len(src)) != 8*hmLen {
-		logger.Errorf("discarding %s, since it has broken hm.m data; got %d bytes; want %d bytes", path, len(src), 8*hmLen)
+	if uint64(len(src)) < 8*hmLen {
+		logger.Errorf("discarding %s, since it has broken hm.m data; got %d bytes; want at least %d bytes", path, len(src), 8*hmLen)
 		return &hourMetricIDs{
+			iidx: newInmemoryInvertedIndex(),
 			hour: hour,
 		}
 	}
@@ -523,9 +544,29 @@ func (s *Storage) mustLoadHourMetricIDs(hour uint64, name string) *hourMetricIDs
 		src = src[8:]
 		m.Add(metricID)
 	}
+
+	// Unmarshal hm.iidx
+	iidx := newInmemoryInvertedIndex()
+	tail, err := iidx.Unmarshal(src)
+	if err != nil {
+		logger.Errorf("discarding %s, since it has broken hm.iidx data: %s", path, err)
+		return &hourMetricIDs{
+			iidx: newInmemoryInvertedIndex(),
+			hour: hour,
+		}
+	}
+	if len(tail) > 0 {
+		logger.Errorf("discarding %s, since it contains superflouos %d bytes of data", path, len(tail))
+		return &hourMetricIDs{
+			iidx: newInmemoryInvertedIndex(),
+			hour: hour,
+		}
+	}
+
 	logger.Infof("loaded %s from %q in %s; entriesCount: %d; sizeBytes: %d", name, path, time.Since(startTime), hmLen, srcOrigLen)
 	return &hourMetricIDs{
 		m:      m,
+		iidx:   iidx,
 		hour:   hourLoaded,
 		isFull: isFull != 0,
 	}
@@ -550,6 +591,10 @@ func (s *Storage) mustSaveHourMetricIDs(hm *hourMetricIDs, name string) {
 	for _, metricID := range hm.m.AppendTo(nil) {
 		dst = encoding.MarshalUint64(dst, metricID)
 	}
+
+	// Marshal hm.iidx
+	dst = hm.iidx.Marshal(dst)
+
 	if err := ioutil.WriteFile(path, dst, 0644); err != nil {
 		logger.Panicf("FATAL: cannot write %d bytes to %q: %s", len(dst), path, err)
 	}
@@ -900,6 +945,7 @@ func (s *Storage) updatePerDateData(rows []rawRow, lastError error) error {
 			s.pendingHourEntriesLock.Lock()
 			s.pendingHourEntries.Add(metricID)
 			s.pendingHourEntriesLock.Unlock()
+			hm.iidx.AddMetricID(idb, metricID)
 		}
 
 		// Slower path: check global cache for (date, metricID) entry.
@@ -908,7 +954,7 @@ func (s *Storage) updatePerDateData(rows []rawRow, lastError error) error {
 			continue
 		}
 
-		// Slow path: store the entry (date, metricID) entry in the indexDB.
+		// Slow path: store the (date, metricID) entry in the indexDB.
 		// It is OK if the (date, metricID) entry is added multiple times to db
 		// by concurrent goroutines.
 		if err := idb.storeDateMetricID(date, metricID); err != nil {
@@ -1077,16 +1123,20 @@ func (s *Storage) updateCurrHourMetricIDs() {
 
 	// Slow path: hm.m must be updated with non-empty s.pendingHourEntries.
 	var m *uint64set.Set
+	var iidx *inmemoryInvertedIndex
 	isFull := hm.isFull
 	if hm.hour == hour {
 		m = hm.m.Clone()
+		iidx = hm.iidx
 	} else {
 		m = &uint64set.Set{}
+		iidx = newInmemoryInvertedIndex()
 		isFull = true
 	}
 	m.Union(newMetricIDs)
 	hmNew := &hourMetricIDs{
 		m:      m,
+		iidx:   iidx,
 		hour:   hour,
 		isFull: isFull,
 	}
@@ -1098,6 +1148,7 @@ func (s *Storage) updateCurrHourMetricIDs() {
 
 type hourMetricIDs struct {
 	m      *uint64set.Set
+	iidx   *inmemoryInvertedIndex
 	hour   uint64
 	isFull bool
 }

lib/storage/storage_test.go

@@ -108,6 +108,7 @@ func TestUpdateCurrHourMetricIDs(t *testing.T) {
 		hour := uint64(timestampFromTime(time.Now())) / msecPerHour
 		hmOrig := &hourMetricIDs{
 			m:    &uint64set.Set{},
+			iidx: newInmemoryInvertedIndex(),
 			hour: 123,
 		}
 		hmOrig.m.Add(12)
@@ -143,6 +144,7 @@ func TestUpdateCurrHourMetricIDs(t *testing.T) {
 		hour := uint64(timestampFromTime(time.Now())) / msecPerHour
 		hmOrig := &hourMetricIDs{
 			m:    &uint64set.Set{},
+			iidx: newInmemoryInvertedIndex(),
 			hour: hour,
 		}
 		hmOrig.m.Add(12)
@@ -187,6 +189,7 @@ func TestUpdateCurrHourMetricIDs(t *testing.T) {
 		hour := uint64(timestampFromTime(time.Now())) / msecPerHour
 		hmOrig := &hourMetricIDs{
 			m:    &uint64set.Set{},
+			iidx: newInmemoryInvertedIndex(),
 			hour: 123,
 		}
 		hmOrig.m.Add(12)
@@ -228,6 +231,7 @@ func TestUpdateCurrHourMetricIDs(t *testing.T) {
 		hour := uint64(timestampFromTime(time.Now())) / msecPerHour
 		hmOrig := &hourMetricIDs{
 			m:    &uint64set.Set{},
+			iidx: newInmemoryInvertedIndex(),
 			hour: hour,
 		}
 		hmOrig.m.Add(12)

lib/uint64set/uint64set.go

@@ -3,6 +3,7 @@ package uint64set
 import (
 	"math/bits"
 	"sort"
+	"unsafe"
 )
 
 // Set is a fast set for uint64.
@@ -47,6 +48,19 @@ func (s *Set) Clone() *Set {
 	return &dst
 }
 
+// SizeBytes returns an estimate size of s in RAM.
+func (s *Set) SizeBytes() uint64 {
+	if s == nil {
+		return 0
+	}
+	n := uint64(unsafe.Sizeof(*s))
+	for _, b := range s.buckets {
+		n += uint64(unsafe.Sizeof(b))
+		n += b.sizeBytes()
+	}
+	return n
+}
+
 // Len returns the number of distinct uint64 values in s.
 func (s *Set) Len() int {
 	if s == nil {
@@ -259,6 +273,16 @@ type bucket32 struct {
 	smallPool     [14]uint32
 }
 
+func (b *bucket32) sizeBytes() uint64 {
+	n := uint64(unsafe.Sizeof(*b))
+	n += 2 * uint64(len(b.b16his))
+	for _, b := range b.buckets {
+		n += uint64(unsafe.Sizeof(b))
+		n += b.sizeBytes()
+	}
+	return n
+}
+
 func (b *bucket32) clone() *bucket32 {
 	var dst bucket32
 	dst.skipSmallPool = b.skipSmallPool
@@ -463,6 +487,10 @@ type bucket16 struct {
 	bits [wordsPerBucket]uint64
 }
 
+func (b *bucket16) sizeBytes() uint64 {
+	return uint64(unsafe.Sizeof(*b))
+}
+
 func (b *bucket16) clone() *bucket16 {
 	var dst bucket16
 	copy(dst.bits[:], b.bits[:])

lib/uint64set/uint64set_test.go

@@ -25,6 +25,9 @@ func testSetBasicOps(t *testing.T, itemsCount int) {
 	// Verify operations on nil set
 	{
 		var sNil *Set
+		if n := sNil.SizeBytes(); n != 0 {
+			t.Fatalf("sNil.SizeBytes must return 0; got %d", n)
+		}
 		if sNil.Has(123) {
 			t.Fatalf("sNil shouldn't contain any item; found 123")
 		}
@@ -73,6 +76,9 @@ func testSetBasicOps(t *testing.T, itemsCount int) {
 	if n := s.Len(); n != itemsCount/2 {
 		t.Fatalf("unexpected s.Len() after forward Add; got %d; want %d", n, itemsCount/2)
 	}
+	if n := s.SizeBytes(); n == 0 {
+		t.Fatalf("s.SizeBytes() must be greater than 0")
+	}
 
 	// Verify backward Add
 	for i := 0; i < itemsCount/2; i++ {
@@ -307,6 +313,9 @@ func testSetSparseItems(t *testing.T, itemsCount int) {
 	if n := s.Len(); n != len(m) {
 		t.Fatalf("unexpected Len(); got %d; want %d", n, len(m))
 	}
+	if n := s.SizeBytes(); n == 0 {
+		t.Fatalf("SizeBytes() must return value greater than 0")
+	}
 
 	// Check Has
 	for x := range m {