lib/streamaggr: improve performance for dedupAggr.sizeBytes() and dedupAggr.itemsCount()

These functions are called every time `/metrics` page is scraped, so it would be great
if they could be sped up for the cases when dedupAggr tracks tens of millions of active time series.

lib/streamaggr/dedup.go

@@ -2,6 +2,7 @@ package streamaggr
 
 import (
 	"sync"
+	"sync/atomic"
 	"unsafe"
 
 	"github.com/cespare/xxhash/v2"
@@ -26,6 +27,9 @@ type dedupAggrShard struct {
 type dedupAggrShardNopad struct {
 	mu sync.Mutex
 	m  map[string]dedupAggrSample
+
+	sizeBytes  atomic.Uint64
+	itemsCount atomic.Uint64
 }
 
 type dedupAggrSample struct {
@@ -43,7 +47,7 @@ func newDedupAggr() *dedupAggr {
 func (da *dedupAggr) sizeBytes() uint64 {
 	n := uint64(unsafe.Sizeof(*da))
 	for i := range da.shards {
-		n += da.shards[i].sizeBytes()
+		n += da.shards[i].sizeBytes.Load()
 	}
 	return n
 }
@@ -51,28 +55,11 @@ func (da *dedupAggr) sizeBytes() uint64 {
 func (da *dedupAggr) itemsCount() uint64 {
 	n := uint64(0)
 	for i := range da.shards {
-		n += da.shards[i].itemsCount()
+		n += da.shards[i].itemsCount.Load()
 	}
 	return n
 }
 
-func (das *dedupAggrShard) sizeBytes() uint64 {
-	das.mu.Lock()
-	n := uint64(unsafe.Sizeof(*das))
-	for k, s := range das.m {
-		n += uint64(len(k)) + uint64(unsafe.Sizeof(k)+unsafe.Sizeof(s))
-	}
-	das.mu.Unlock()
-	return n
-}
-
-func (das *dedupAggrShard) itemsCount() uint64 {
-	das.mu.Lock()
-	n := uint64(len(das.m))
-	das.mu.Unlock()
-	return n
-}
-
 func (da *dedupAggr) pushSamples(samples []pushSample) {
 	pss := getPerShardSamples()
 	shards := pss.shards
@@ -181,6 +168,8 @@ func (das *dedupAggrShard) pushSamples(samples []pushSample) {
 				value:     sample.value,
 				timestamp: sample.timestamp,
 			}
+			das.itemsCount.Add(1)
+			das.sizeBytes.Add(uint64(len(key)) + uint64(unsafe.Sizeof("")+unsafe.Sizeof(dedupAggrSample{})))
 			continue
 		}
 		// Update the existing value according to logic described at https://docs.victoriametrics.com/#deduplication
@@ -200,6 +189,8 @@ func (das *dedupAggrShard) flush(ctx *dedupFlushCtx, f func(samples []pushSample
 	m := das.m
 	if len(m) > 0 {
 		das.m = make(map[string]dedupAggrSample, len(m))
+		das.sizeBytes.Store(0)
+		das.itemsCount.Store(0)
 	}
 
 	das.mu.Unlock()