volume: add "hasSlowRead" option to customize read optimization

weed/command/server.go

@@ -131,6 +131,7 @@ func init() {
 	serverOptions.v.pprof = cmdServer.Flag.Bool("volume.pprof", false, "enable pprof http handlers. precludes --memprofile and --cpuprofile")
 	serverOptions.v.idxFolder = cmdServer.Flag.String("volume.dir.idx", "", "directory to store .idx files")
 	serverOptions.v.inflightUploadDataTimeout = cmdServer.Flag.Duration("volume.inflightUploadDataTimeout", 60*time.Second, "inflight upload data wait timeout of volume servers")
+	serverOptions.v.hasSlowRead = cmdServer.Flag.Bool("volume.hasSlowRead", false, "if true, this prevents slow reads from blocking other requests, but large file read P99 latency will increase.")
 
 	s3Options.port = cmdServer.Flag.Int("s3.port", 8333, "s3 server http listen port")
 	s3Options.portGrpc = cmdServer.Flag.Int("s3.port.grpc", 0, "s3 server grpc listen port")

weed/command/volume.go

@@ -66,6 +66,7 @@ type VolumeServerOptions struct {
 	metricsHttpPort           *int
 	// pulseSeconds          *int
 	inflightUploadDataTimeout *time.Duration
+	hasSlowRead               *bool
 }
 
 func init() {
@@ -96,6 +97,7 @@ func init() {
 	v.metricsHttpPort = cmdVolume.Flag.Int("metricsPort", 0, "Prometheus metrics listen port")
 	v.idxFolder = cmdVolume.Flag.String("dir.idx", "", "directory to store .idx files")
 	v.inflightUploadDataTimeout = cmdVolume.Flag.Duration("inflightUploadDataTimeout", 60*time.Second, "inflight upload data wait timeout of volume servers")
+	v.hasSlowRead = cmdVolume.Flag.Bool("hasSlowRead", false, "if true, this prevents slow reads from blocking other requests, but large file read P99 latency will increase.")
 }
 
 var cmdVolume = &Command{
@@ -243,6 +245,7 @@ func (v VolumeServerOptions) startVolumeServer(volumeFolders, maxVolumeCounts, v
 		int64(*v.concurrentUploadLimitMB)*1024*1024,
 		int64(*v.concurrentDownloadLimitMB)*1024*1024,
 		*v.inflightUploadDataTimeout,
+		*v.hasSlowRead,
 	)
 	// starting grpc server
 	grpcS := v.startGrpcService(volumeServer)

weed/server/volume_server.go

@@ -28,6 +28,7 @@ type VolumeServer struct {
 	inFlightUploadDataLimitCond   *sync.Cond
 	inFlightDownloadDataLimitCond *sync.Cond
 	inflightUploadDataTimeout     time.Duration
+	hasSlowRead                   bool
 
 	SeedMasterNodes []pb.ServerAddress
 	currentMaster   pb.ServerAddress
@@ -64,6 +65,7 @@ func NewVolumeServer(adminMux, publicMux *http.ServeMux, ip string,
 	concurrentUploadLimit int64,
 	concurrentDownloadLimit int64,
 	inflightUploadDataTimeout time.Duration,
+	hasSlowRead bool,
 ) *VolumeServer {
 
 	v := util.GetViper()
@@ -93,6 +95,7 @@ func NewVolumeServer(adminMux, publicMux *http.ServeMux, ip string,
 		concurrentUploadLimit:         concurrentUploadLimit,
 		concurrentDownloadLimit:       concurrentDownloadLimit,
 		inflightUploadDataTimeout:     inflightUploadDataTimeout,
+		hasSlowRead:                   hasSlowRead,
 	}
 	vs.SeedMasterNodes = masterNodes
 

weed/server/volume_server_handlers_read.go

@@ -117,6 +117,7 @@ func (vs *VolumeServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request)
 
 	readOption := &storage.ReadOption{
 		ReadDeleted: r.FormValue("readDeleted") == "true",
+		HasSlowRead: vs.hasSlowRead,
 	}
 
 	var count int

weed/storage/store.go

@@ -35,6 +35,15 @@ type ReadOption struct {
 	IsMetaOnly     bool // read status
 	VolumeRevision uint16
 	IsOutOfRange   bool // whether read over MaxPossibleVolumeSize
+
+	// If HasSlowRead is set to true:
+	//  * read requests and write requests compete for the lock.
+	//  * large file read P99 latency on busy sites will go up, due to the need to get locks multiple times.
+	//  * write requests will see lower latency.
+	// If HasSlowRead is set to false:
+	//  * read requests should complete asap, not blocking other requests.
+	//  * write requests may see high latency when downloading large files.
+	HasSlowRead bool
 }
 
 /*

weed/storage/volume_read.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"github.com/seaweedfs/seaweedfs/weed/util/mem"
 	"io"
+	"sync"
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
@@ -101,9 +102,18 @@ func (v *Volume) readNeedleMetaAt(n *needle.Needle, offset int64, size int32) (e
 // read fills in Needle content by looking up n.Id from NeedleMapper
 func (v *Volume) readNeedleDataInto(n *needle.Needle, readOption *ReadOption, writer io.Writer, offset int64, size int64) (err error) {
 
-	v.dataFileAccessLock.RLock()
+	if !readOption.HasSlowRead {
+		v.dataFileAccessLock.RLock()
+		defer v.dataFileAccessLock.RUnlock()
+	}
+
+	if readOption.HasSlowRead {
+		v.dataFileAccessLock.RLock()
+	}
 	nv, ok := v.nm.Get(n.Id)
-	v.dataFileAccessLock.RUnlock()
+	if readOption.HasSlowRead {
+		v.dataFileAccessLock.RUnlock()
+	}
 
 	if !ok || nv.Offset.IsZero() {
 		return ErrorNotFound
@@ -133,20 +143,26 @@ func (v *Volume) readNeedleDataInto(n *needle.Needle, readOption *ReadOption, wr
 	crc := needle.CRC(0)
 	for x := offset; x < offset+size; x += int64(len(buf)) {
 
-		v.dataFileAccessLock.RLock()
+		if readOption.HasSlowRead {
+			v.dataFileAccessLock.RLock()
+		}
 		// possibly re-read needle offset if volume is compacted
 		if readOption.VolumeRevision != v.SuperBlock.CompactionRevision {
 			// the volume is compacted
 			nv, ok = v.nm.Get(n.Id)
 			if !ok || nv.Offset.IsZero() {
-				v.dataFileAccessLock.RUnlock()
+				if readOption.HasSlowRead {
+					v.dataFileAccessLock.RUnlock()
+				}
 				return ErrorNotFound
 			}
 			actualOffset = nv.Offset.ToActualOffset()
 			readOption.VolumeRevision = v.SuperBlock.CompactionRevision
 		}
 		count, err := n.ReadNeedleData(v.DataBackend, actualOffset, buf, x)
-		v.dataFileAccessLock.RUnlock()
+		if readOption.HasSlowRead {
+			v.dataFileAccessLock.RUnlock()
+		}
 
 		toWrite := min(count, int(offset+size-x))
 		if toWrite > 0 {
@@ -174,6 +190,14 @@ func (v *Volume) readNeedleDataInto(n *needle.Needle, readOption *ReadOption, wr
 
 }
 
+func synchronizedRead(rwLock *sync.RWMutex, enabled bool, closure func() error) error {
+	if enabled {
+		rwLock.RLock()
+		defer rwLock.RUnlock()
+	}
+	return closure()
+}
+
 func min(x, y int) int {
 	if x < y {
 		return x