lib/logstorage: improve the performance of obtaining _stream column value

Substitute global streamTagsCache with per-blockSearch cache for ((stream.id) -> (_stream value)) entries.
This improves scalability of obtaining _stream values on a machine with many CPU cores, since every CPU
has its own blockSearch instance.

This also should reduce memory usage when querying logs over big number of streams, since per-blockSearch
cache of ((stream.id) -> (_stream value)) entries is limited in size, and its lifetime is bounded by a single query.

lib/logstorage/block_result.go

@@ -500,43 +500,11 @@ func (br *blockResult) addStreamIDColumn(bs *blockSearch) {
 }
 
 func (br *blockResult) addStreamColumn(bs *blockSearch) bool {
-	if !bs.prevStreamID.equal(&bs.bsw.bh.streamID) {
-		return br.addStreamColumnSlow(bs)
-	}
-
-	if len(bs.prevStream) == 0 {
+	streamStr := bs.getStreamStr()
+	if streamStr == "" {
 		return false
 	}
-	br.addConstColumn("_stream", bytesutil.ToUnsafeString(bs.prevStream))
-	return true
-}
-
-func (br *blockResult) addStreamColumnSlow(bs *blockSearch) bool {
-	bb := bbPool.Get()
-	defer bbPool.Put(bb)
-
-	streamID := &bs.bsw.bh.streamID
-	bb.B = bs.bsw.p.pt.appendStreamTagsByStreamID(bb.B[:0], streamID)
-	if len(bb.B) == 0 {
-		// Couldn't find stream tags by streamID. This may be the case when the corresponding log stream
-		// was recently registered and its tags aren't visible to search yet.
-		// The stream tags must become visible in a few seconds.
-		// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6042
-		bs.prevStreamID = *streamID
-		bs.prevStream = bs.prevStream[:0]
-		return false
-	}
-
-	st := GetStreamTags()
-	mustUnmarshalStreamTags(st, bb.B)
-	bb.B = st.marshalString(bb.B[:0])
-	PutStreamTags(st)
-
-	s := bytesutil.ToUnsafeString(bb.B)
-	br.addConstColumn("_stream", s)
-
-	bs.prevStreamID = *streamID
-	bs.prevStream = append(bs.prevStream[:0], s...)
+	br.addConstColumn("_stream", streamStr)
 	return true
 }
 

lib/logstorage/block_search.go

@@ -85,6 +85,10 @@ func getBlockSearch() *blockSearch {
 
 func putBlockSearch(bs *blockSearch) {
 	bs.reset()
+
+	// reset seenStreams before returning bs to the pool in order to reduce memory usage.
+	bs.seenStreams = nil
+
 	blockSearchPool.Put(bs)
 }
 
@@ -115,10 +119,9 @@ type blockSearch struct {
 	// a is used for storing unmarshaled data in csh
 	a arena
 
-	// prevStreamID and prevStream are used for speeding up fetching _stream columns
-	// across sequential blocks belonging to the same stream.
-	prevStreamID streamID
-	prevStream   []byte
+	// seenStreams contains seen streamIDs for the recent searches.
+	// It is used for speeding up fetching _stream column.
+	seenStreams map[u128]string
 }
 
 func (bs *blockSearch) reset() {
@@ -145,6 +148,8 @@ func (bs *blockSearch) reset() {
 	bs.sbu.reset()
 	bs.csh.reset()
 	bs.a.reset()
+
+	// Do not reset seenStreams, since its' lifetime is managed by blockResult.addStreamColumn() code.
 }
 
 func (bs *blockSearch) partPath() string {
@@ -326,3 +331,48 @@ func (ih *indexBlockHeader) mustReadBlockHeaders(dst []blockHeader, p *part) []b
 
 	return dst
 }
+
+// getStreamStr returns _stream value for the given block at bs.
+func (bs *blockSearch) getStreamStr() string {
+	sid := bs.bsw.bh.streamID.id
+	streamStr := bs.seenStreams[sid]
+	if streamStr != "" {
+		// Fast path - streamStr is found in the seenStreams.
+		return streamStr
+	}
+
+	// Slow path - load streamStr from the storage.
+	streamStr = bs.getStreamStrSlow()
+	if streamStr != "" {
+		// Store the found streamStr in seenStreams.
+		if len(bs.seenStreams) > 20_000 {
+			bs.seenStreams = nil
+		}
+		if bs.seenStreams == nil {
+			bs.seenStreams = make(map[u128]string)
+		}
+		bs.seenStreams[sid] = streamStr
+	}
+	return streamStr
+}
+
+func (bs *blockSearch) getStreamStrSlow() string {
+	bb := bbPool.Get()
+	defer bbPool.Put(bb)
+
+	bb.B = bs.bsw.p.pt.idb.appendStreamTagsByStreamID(bb.B[:0], &bs.bsw.bh.streamID)
+	if len(bb.B) == 0 {
+		// Couldn't find stream tags by sid. This may be the case when the corresponding log stream
+		// was recently registered and its tags aren't visible to search yet.
+		// The stream tags must become visible in a few seconds.
+		// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6042
+		return ""
+	}
+
+	st := GetStreamTags()
+	mustUnmarshalStreamTags(st, bb.B)
+	bb.B = st.marshalString(bb.B[:0])
+	PutStreamTags(st)
+
+	return string(bb.B)
+}

lib/logstorage/partition.go

@@ -159,32 +159,6 @@ func (pt *partition) logIngestedRows(lr *LogRows) {
 	}
 }
 
-// appendStreamTagsByStreamID appends canonical representation of stream tags for the given sid to dst
-// and returns the result.
-func (pt *partition) appendStreamTagsByStreamID(dst []byte, sid *streamID) []byte {
-	// Search for the StreamTags in the cache.
-	key := bbPool.Get()
-	defer bbPool.Put(key)
-
-	// There is no need in putting partition name into key here,
-	// since StreamTags is uniquely identified by streamID.
-	key.B = sid.marshal(key.B)
-	dstLen := len(dst)
-	dst = pt.s.streamTagsCache.GetBig(dst, key.B)
-	if len(dst) > dstLen {
-		// Fast path - the StreamTags have been found in cache.
-		return dst
-	}
-
-	// Slow path - search for StreamTags in idb
-	dst = pt.idb.appendStreamTagsByStreamID(dst, sid)
-	if len(dst) > dstLen {
-		// Store the found StreamTags to cache
-		pt.s.streamTagsCache.SetBig(key.B, dst[dstLen:])
-	}
-	return dst
-}
-
 func (pt *partition) hasStreamIDInCache(sid *streamID) bool {
 	var result [1]byte
 

lib/logstorage/storage.go

@@ -135,15 +135,6 @@ type Storage struct {
 	// the check whether the given stream is already registered in the persistent storage.
 	streamIDCache *workingsetcache.Cache
 
-	// streamTagsCache caches StreamTags entries keyed by streamID.
-	//
-	// There is no need to put partition into the key for StreamTags,
-	// since StreamTags are uniquely identified by streamID.
-	//
-	// It reduces the load on persistent storage during querying
-	// when StreamTags must be found for the particular streamID
-	streamTagsCache *workingsetcache.Cache
-
 	// filterStreamCache caches streamIDs keyed by (partition, []TenanID, StreamFilter).
 	//
 	// It reduces the load on persistent storage during querying by _stream:{...} filter.
@@ -253,8 +244,6 @@ func MustOpenStorage(path string, cfg *StorageConfig) *Storage {
 	streamIDCachePath := filepath.Join(path, cacheDirname, streamIDCacheFilename)
 	streamIDCache := workingsetcache.Load(streamIDCachePath, mem/16)
 
-	streamTagsCache := workingsetcache.New(mem / 10)
-
 	filterStreamCache := workingsetcache.New(mem / 10)
 
 	s := &Storage{
@@ -270,7 +259,6 @@ func MustOpenStorage(path string, cfg *StorageConfig) *Storage {
 		stopCh:                 make(chan struct{}),
 
 		streamIDCache:     streamIDCache,
-		streamTagsCache:   streamTagsCache,
 		filterStreamCache: filterStreamCache,
 	}
 
@@ -474,9 +462,6 @@ func (s *Storage) MustClose() {
 	s.streamIDCache.Stop()
 	s.streamIDCache = nil
 
-	s.streamTagsCache.Stop()
-	s.streamTagsCache = nil
-
 	s.filterStreamCache.Stop()
 	s.filterStreamCache = nil