lib/storage: optimize per-day inverted index search for tag filters matching big number of time series

- Sort tag filters in the ascending number of matching time series
  in order to apply the most specific filters first.
- Fall back to metricName search for filters matching big number of time series
  (usually this are negative filters or regexp filters).

lib/storage/index_db.go

@@ -126,10 +126,14 @@ type indexDB struct {
 	// Cache for fast MetricID -> MetricName lookup.
 	metricNameCache *workingsetcache.Cache
 
-	// Cache holding useless TagFilters entries, which have no tag filters
+	// Cache for useless TagFilters entries, which have no tag filters
 	// matching low number of metrics.
 	uselessTagFiltersCache *workingsetcache.Cache
 
+	// Cache for (date, tagFilter) -> metricIDsLen, which is used for reducing
+	// the amount of work when matching a set of filters.
+	metricIDsPerDateTagFilterCache *workingsetcache.Cache
+
 	indexSearchPool sync.Pool
 
 	// An inmemory set of deleted metricIDs.
@@ -182,6 +186,7 @@ func openIndexDB(path string, metricIDCache, metricNameCache *workingsetcache.Ca
 		metricIDCache:                  metricIDCache,
 		metricNameCache:                metricNameCache,
 		uselessTagFiltersCache:         workingsetcache.New(mem/128, time.Hour),
+		metricIDsPerDateTagFilterCache: workingsetcache.New(mem/128, time.Hour),
 
 		currHourMetricIDs: currHourMetricIDs,
 		prevHourMetricIDs: prevHourMetricIDs,
@@ -348,11 +353,13 @@ func (db *indexDB) decRef() {
 	// Free space occupied by caches owned by db.
 	db.tagCache.Stop()
 	db.uselessTagFiltersCache.Stop()
+	db.metricIDsPerDateTagFilterCache.Stop()
 
 	db.tagCache = nil
 	db.metricIDCache = nil
 	db.metricNameCache = nil
 	db.uselessTagFiltersCache = nil
+	db.metricIDsPerDateTagFilterCache = nil
 
 	if atomic.LoadUint64(&db.mustDrop) == 0 {
 		return
@@ -1053,8 +1060,7 @@ func (is *indexSearch) getStartDateForPerDayInvertedIndex() (uint64, error) {
 	if err := ts.Error(); err != nil {
 		return 0, err
 	}
-	// The minDate can contain incomplete inverted index, so increment it.
-	minDate++
+	// There are no (date,tag)->metricIDs entries in the database yet.
 	return minDate, nil
 }
 
@@ -1700,22 +1706,8 @@ func (is *indexSearch) searchMetricIDs(tfss []*TagFilters, tr TimeRange, maxMetr
 func (is *indexSearch) updateMetricIDsForTagFilters(metricIDs *uint64set.Set, tfs *TagFilters, tr TimeRange, maxMetrics int) error {
 	// Sort tag filters for faster ts.Seek below.
 	sort.Slice(tfs.tfs, func(i, j int) bool {
-		// Move regexp and negative filters to the end, since they require scanning
-		// all the entries for the given label.
-		a := &tfs.tfs[i]
-		b := &tfs.tfs[j]
-		if a.isRegexp != b.isRegexp {
-			return !a.isRegexp
-		}
-		if a.isNegative != b.isNegative {
-			return !a.isNegative
-		}
-		if len(a.orSuffixes) != len(b.orSuffixes) {
-			return len(a.orSuffixes) < len(b.orSuffixes)
-		}
-		return bytes.Compare(a.prefix, b.prefix) < 0
+		return tfs.tfs[i].Less(&tfs.tfs[j])
 	})
-
 	err := is.tryUpdatingMetricIDsForDateRange(metricIDs, tfs, tr, maxMetrics)
 	if err == nil {
 		// Fast path: found metricIDs by date range.
@@ -2177,10 +2169,40 @@ func (is *indexSearch) tryUpdatingMetricIDsForDateRange(metricIDs *uint64set.Set
 }
 
 func (is *indexSearch) getMetricIDsForDateAndFilters(date uint64, tfs *TagFilters, maxMetrics int) (*uint64set.Set, error) {
-	// Populate metricIDs with the first non-negative filter.
-	var tfFirst *tagFilter
+	// Sort tfs by the number of matching filters from previous queries.
+	// This way we limit the amount of work below by applying more specific filters at first.
+	type tagFilterWithCount struct {
+		tf    *tagFilter
+		count uint64
+	}
+	tfsWithCount := make([]tagFilterWithCount, len(tfs.tfs))
+	kb := &is.kb
+	var buf []byte
 	for i := range tfs.tfs {
 		tf := &tfs.tfs[i]
+		kb.B = appendDateTagFilterCacheKey(kb.B[:0], date, tf, tfs.accountID, tfs.projectID)
+		buf = is.db.metricIDsPerDateTagFilterCache.Get(buf[:0], kb.B)
+		count := uint64(0)
+		if len(buf) == 8 {
+			count = encoding.UnmarshalUint64(buf)
+		}
+		tfsWithCount[i] = tagFilterWithCount{
+			tf:    tf,
+			count: count,
+		}
+	}
+	sort.Slice(tfsWithCount, func(i, j int) bool {
+		a, b := &tfsWithCount[i], &tfsWithCount[j]
+		if a.count != b.count {
+			return a.count < b.count
+		}
+		return a.tf.Less(b.tf)
+	})
+
+	// Populate metricIDs with the first non-negative filter.
+	var tfFirst *tagFilter
+	for i := range tfsWithCount {
+		tf := tfsWithCount[i].tf
 		if tf.isNegative {
 			continue
 		}
@@ -2217,11 +2239,30 @@ func (is *indexSearch) getMetricIDsForDateAndFilters(date uint64, tfs *TagFilter
 	}
 
 	// Intersect metricIDs with the rest of filters.
-	for i := range tfs.tfs {
-		tf := &tfs.tfs[i]
+	for i := range tfsWithCount {
+		tfWithCount := &tfsWithCount[i]
+		tf := tfWithCount.tf
 		if tf == tfFirst {
 			continue
 		}
+		if n := uint64(metricIDs.Len()); n < 1000 || n < tfWithCount.count/maxIndexScanLoopsPerMetric {
+			// It should be faster performing metricName match on the remaining filters
+			// instead of scanning big number of entries in the inverted index for these filters.
+			tfsRemaining := tfsWithCount[i:]
+			tfsPostponed := make([]*tagFilter, 0, len(tfsRemaining))
+			for j := range tfsRemaining {
+				tf := tfsRemaining[j].tf
+				if tf == tfFirst {
+					continue
+				}
+				tfsPostponed = append(tfsPostponed, tf)
+			}
+			var m uint64set.Set
+			if err := is.updateMetricIDsByMetricNameMatch(&m, metricIDs, tfsPostponed, tfs.accountID, tfs.projectID); err != nil {
+				return nil, err
+			}
+			return &m, nil
+		}
 		m, err := is.getMetricIDsForDateTagFilter(tf, date, tfs.commonPrefix, tfs.accountID, tfs.projectID, maxDateMetrics)
 		if err != nil {
 			return nil, err
@@ -2376,7 +2417,26 @@ func (is *indexSearch) getMetricIDsForDateTagFilter(tf *tagFilter, date uint64,
 	tfNew := *tf
 	tfNew.isNegative = false // isNegative for the original tf is handled by the caller.
 	tfNew.prefix = kb.B
-	return is.getMetricIDsForTagFilter(&tfNew, maxMetrics)
+	metricIDs, err := is.getMetricIDsForTagFilter(&tfNew, maxMetrics)
+
+	// Store the number of matching metricIDs in the cache in order to sort tag filters
+	// in ascending number of matching metricIDs on the next search.
+	is.kb.B = appendDateTagFilterCacheKey(is.kb.B[:0], date, tf, accountID, projectID)
+	metricIDsLen := uint64(metricIDs.Len())
+	if err != nil {
+		// Set metricIDsLen to maxMetrics, so the given entry will be moved to the end
+		// of tag filters on the next search.
+		metricIDsLen = uint64(maxMetrics)
+	}
+	kb.B = encoding.MarshalUint64(kb.B[:0], metricIDsLen)
+	is.db.metricIDsPerDateTagFilterCache.Set(is.kb.B, kb.B)
+	return metricIDs, err
+}
+
+func appendDateTagFilterCacheKey(dst []byte, date uint64, tf *tagFilter, accountID, projectID uint32) []byte {
+	dst = encoding.MarshalUint64(dst, date)
+	dst = tf.Marshal(dst, accountID, projectID)
+	return dst
 }
 
 func (is *indexSearch) getMetricIDsForDate(date uint64, accountID, projectID uint32, maxMetrics int) (*uint64set.Set, error) {
@@ -2444,7 +2504,7 @@ func (is *indexSearch) updateMetricIDsForPrefix(prefix []byte, metricIDs *uint64
 // over the found metrics.
 const maxIndexScanLoopsPerMetric = 100
 
-// The maximum number of slow index scan loops per.
+// The maximum number of slow index scan loops.
 // Bigger number of loops is slower than updateMetricIDsByMetricNameMatch
 // over the found metrics.
 const maxIndexScanSlowLoopsPerMetric = 20

lib/storage/tag_filters.go

@@ -160,6 +160,21 @@ type tagFilter struct {
 	matchesEmptyValue bool
 }
 
+func (tf *tagFilter) Less(other *tagFilter) bool {
+	// Move regexp and negative filters to the end, since they require scanning
+	// all the entries for the given label.
+	if tf.isRegexp != other.isRegexp {
+		return !tf.isRegexp
+	}
+	if tf.isNegative != other.isNegative {
+		return !tf.isNegative
+	}
+	if len(tf.orSuffixes) != len(other.orSuffixes) {
+		return len(tf.orSuffixes) < len(other.orSuffixes)
+	}
+	return bytes.Compare(tf.prefix, other.prefix) < 0
+}
+
 // String returns human-readable tf value.
 func (tf *tagFilter) String() string {
 	op := "="