fix: re-use bytes.Buffer using sync.Pool (#11156)

cmd/metacache-bucket.go

@@ -113,6 +113,7 @@ func loadBucketMetaCache(ctx context.Context, bucket string) (*bucketMetacache,
 	// Use global context for this.
 	err := objAPI.GetObject(GlobalContext, minioMetaBucket, pathJoin("buckets", bucket, ".metacache", "index.s2"), 0, -1, w, "", ObjectOptions{})
 	logger.LogIf(ctx, w.CloseWithError(err))
+	wg.Wait()
 	if err != nil {
 		switch err.(type) {
 		case ObjectNotFound:
@@ -125,7 +126,6 @@ func loadBucketMetaCache(ctx context.Context, bucket string) (*bucketMetacache,
 		}
 		return newBucketMetacache(bucket, false), err
 	}
-	wg.Wait()
 	if decErr != nil {
 		if errors.Is(err, context.Canceled) {
 			return newBucketMetacache(bucket, false), err

cmd/metacache-set.go

@@ -432,7 +432,11 @@ func (er *erasureObjects) streamMetadataParts(ctx context.Context, o listPathOpt
 
 		// We got a stream to start at.
 		loadedPart := 0
-		var buf bytes.Buffer
+		buf := bufferPool.Get().(*bytes.Buffer)
+		defer func() {
+			buf.Reset()
+			bufferPool.Put(buf)
+		}()
 		for {
 			select {
 			case <-ctx.Done():
@@ -482,7 +486,7 @@ func (er *erasureObjects) streamMetadataParts(ctx context.Context, o listPathOpt
 				}
 			}
 			buf.Reset()
-			err := er.getObjectWithFileInfo(ctx, minioMetaBucket, o.objectPath(partN), 0, fi.Size, &buf, fi, metaArr, onlineDisks)
+			err := er.getObjectWithFileInfo(ctx, minioMetaBucket, o.objectPath(partN), 0, fi.Size, buf, fi, metaArr, onlineDisks)
 			if err != nil {
 				switch toObjectErr(err, minioMetaBucket, o.objectPath(partN)).(type) {
 				case ObjectNotFound:
@@ -498,7 +502,7 @@ func (er *erasureObjects) streamMetadataParts(ctx context.Context, o listPathOpt
 					return entries, err
 				}
 			}
-			tmp, err := newMetacacheReader(&buf)
+			tmp, err := newMetacacheReader(buf)
 			if err != nil {
 				return entries, err
 			}

cmd/metacache-stream.go

@@ -745,6 +745,12 @@ type metacacheBlockWriter struct {
 	blockEntries int
 }
 
+var bufferPool = sync.Pool{
+	New: func() interface{} {
+		return new(bytes.Buffer)
+	},
+}
+
 // newMetacacheBlockWriter provides a streaming block writer.
 // Each block is the size of the capacity of the input channel.
 // The caller should close to indicate the stream has ended.
@@ -755,12 +761,15 @@ func newMetacacheBlockWriter(in <-chan metaCacheEntry, nextBlock func(b *metacac
 		defer w.wg.Done()
 		var current metacacheBlock
 		var n int
-		var buf bytes.Buffer
-		block := newMetacacheWriter(&buf, 1<<20)
+		buf := bufferPool.Get().(*bytes.Buffer)
+		defer func() {
+			buf.Reset()
+			bufferPool.Put(buf)
+		}()
+		block := newMetacacheWriter(buf, 1<<20)
 		defer block.Close()
 		finishBlock := func() {
-			err := block.Close()
-			if err != nil {
+			if err := block.Close(); err != nil {
 				w.streamErr = err
 				return
 			}
@@ -769,7 +778,7 @@ func newMetacacheBlockWriter(in <-chan metaCacheEntry, nextBlock func(b *metacac
 			// Prepare for next
 			current.n++
 			buf.Reset()
-			block.Reset(&buf)
+			block.Reset(buf)
 			current.First = ""
 		}
 		for o := range in {