filer.sync: show active chunk transfers when sync progress stalls

When the sync watermark is not advancing, print each in-progress chunk
transfer with its file path, bytes received so far, and current status
(downloading, uploading, or waiting with backoff duration). This helps
diagnose which files are blocking progress during replication.

Closes #8542

weed/command/filer_sync.go

@@ -359,6 +359,7 @@ func doSubscribeFilerMetaChanges(clientId int32, clientEpoch int32, sourceGrpcDi
 	}
 
 	var lastLogTsNs = time.Now().UnixNano()
+	var lastProgressedTsNs int64
 	var clientName = fmt.Sprintf("syncFrom_%s_To_%s", string(sourceFiler), string(targetFiler))
 	processEventFnWithOffset := pb.AddOffsetFunc(func(resp *filer_pb.SubscribeMetadataResponse) error {
 		processor.AddSyncJob(resp)
@@ -372,6 +373,13 @@ func doSubscribeFilerMetaChanges(clientId int32, clientEpoch int32, sourceGrpcDi
 		now := time.Now().UnixNano()
 		glog.V(0).Infof("sync %s to %s progressed to %v %0.2f/sec", sourceFiler, targetFiler, time.Unix(0, offsetTsNs), float64(counter)/(float64(now-lastLogTsNs)/1e9))
 		lastLogTsNs = now
+		if offsetTsNs == lastProgressedTsNs {
+			for _, t := range filerSink.ActiveTransfers() {
+				glog.V(0).Infof("  %s %s: %d bytes received, %s",
+					t.ChunkFileId, t.Path, t.BytesReceived, t.Status)
+			}
+		}
+		lastProgressedTsNs = offsetTsNs
 		// collect synchronous offset
 		statsCollect.FilerSyncOffsetGauge.WithLabelValues(sourceFiler.String(), targetFiler.String(), clientName, sourcePath).Set(float64(offsetTsNs))
 		return setOffset(targetGrpcDialOption, targetFiler, getSignaturePrefixByPath(sourcePath), sourceFilerSignature, offsetTsNs)

weed/replication/sink/filersink/fetch_write.go

@@ -241,6 +241,14 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 		return "", fmt.Errorf("upload data: %w", err)
 	}
 
+	transferStatus := &ChunkTransferStatus{
+		ChunkFileId: sourceChunk.GetFileIdString(),
+		Path:        path,
+		Status:      "downloading",
+	}
+	fs.activeTransfers.Store(sourceChunk.GetFileIdString(), transferStatus)
+	defer fs.activeTransfers.Delete(sourceChunk.GetFileIdString())
+
 	eofBackoff := time.Duration(0)
 	var partialData []byte
 	var savedFilename string
@@ -282,6 +290,9 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 			fullData = data
 		}
 
+		transferStatus.BytesReceived = int64(len(fullData))
+		transferStatus.Status = "uploading"
+
 		currentFileId, uploadResult, uploadErr, _ := uploader.UploadWithRetry(
 			fs,
 			&filer_pb.AssignVolumeRequest{
@@ -326,9 +337,12 @@ func (fs *FilerSink) fetchAndWrite(sourceChunk *filer_pb.FileChunk, path string,
 		}
 		if isEofError(retryErr) {
 			eofBackoff = nextEofBackoff(eofBackoff)
+			transferStatus.BytesReceived = int64(len(partialData))
+			transferStatus.Status = fmt.Sprintf("waiting %v", eofBackoff)
 			glog.V(0).Infof("source connection interrupted while replicating %s for %s (%d bytes received so far), backing off %v: %v",
 				sourceChunk.GetFileIdString(), path, len(partialData), eofBackoff, retryErr)
 			time.Sleep(eofBackoff)
+			transferStatus.Status = "downloading"
 		} else {
 			glog.V(0).Infof("replicate %s for %s: %v", sourceChunk.GetFileIdString(), path, retryErr)
 		}

weed/replication/sink/filersink/filer_sink.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"math"
+	"sync"
 
 	"github.com/seaweedfs/seaweedfs/weed/pb"
 	"github.com/seaweedfs/seaweedfs/weed/wdclient"
@@ -20,6 +21,14 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/util"
 )
 
+// ChunkTransferStatus tracks the progress of a single chunk being replicated.
+type ChunkTransferStatus struct {
+	ChunkFileId   string
+	Path          string
+	BytesReceived int64
+	Status        string // "downloading", "uploading", or "waiting 10s" etc.
+}
+
 type FilerSink struct {
 	filerSource       *source.FilerSource
 	grpcAddress       string
@@ -35,6 +44,7 @@ type FilerSink struct {
 	isIncremental     bool
 	executor          *util.LimitedConcurrentExecutor
 	signature         int32
+	activeTransfers   sync.Map // chunkFileId -> *ChunkTransferStatus
 }
 
 func init() {
@@ -101,6 +111,16 @@ func (fs *FilerSink) SetChunkConcurrency(concurrency int) {
 	}
 }
 
+// ActiveTransfers returns a snapshot of all in-progress chunk transfers.
+func (fs *FilerSink) ActiveTransfers() []*ChunkTransferStatus {
+	var transfers []*ChunkTransferStatus
+	fs.activeTransfers.Range(func(key, value any) bool {
+		transfers = append(transfers, value.(*ChunkTransferStatus))
+		return true
+	})
+	return transfers
+}
+
 func (fs *FilerSink) DeleteEntry(key string, isDirectory, deleteIncludeChunks bool, signatures []int32) error {
 
 	dir, name := util.FullPath(key).DirAndName()