[#1143] shard: Introduce explicit Degraded mode

`Degraded` mode is set automatically after error counter is over the
threshold. `ReadOnly` mode can still be set by an administrator.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

cmd/neofs-cli/modules/control.go

@@ -78,6 +78,7 @@ const (
 
 	shardModeReadOnly  = "read-only"
 	shardModeReadWrite = "read-write"
+	shardModeDegraded  = "degraded"
 )
 
 const (
@@ -124,9 +125,10 @@ func initControlSetShardModeCmd() {
 	flags.String(controlRPC, controlRPCDefault, controlRPCUsage)
 	flags.StringVarP(&shardID, shardIDFlag, "", "", "ID of the shard in base58 encoding")
 	flags.StringVarP(&shardMode, shardModeFlag, "", "",
-		fmt.Sprintf("new shard mode keyword ('%s', '%s')",
+		fmt.Sprintf("new shard mode keyword ('%s', '%s', '%s')",
 			shardModeReadWrite,
 			shardModeReadOnly,
+			shardModeDegraded,
 		),
 	)
 	flags.Bool(shardClearErrorsFlag, false, "Set shard error count to 0")
@@ -490,6 +492,8 @@ func prettyPrintShards(cmd *cobra.Command, ii []*control.ShardInfo) {
 			mode = "read-write"
 		case control.ShardMode_READ_ONLY:
 			mode = "read-only"
+		case control.ShardMode_DEGRADED:
+			mode = "degraded"
 		default:
 			mode = "unknown"
 		}
@@ -526,6 +530,8 @@ func setShardMode(cmd *cobra.Command, _ []string) {
 		mode = control.ShardMode_READ_WRITE
 	case shardModeReadOnly:
 		mode = control.ShardMode_READ_ONLY
+	case shardModeDegraded:
+		mode = control.ShardMode_DEGRADED
 	}
 
 	req := new(control.SetShardModeRequest)

cmd/neofs-node/config/engine/shard/config.go

@@ -77,6 +77,8 @@ func (x *Config) Mode() (m shard.Mode) {
 		m = shard.ModeReadWrite
 	case "read-only":
 		m = shard.ModeReadOnly
+	case "degraded":
+		m = shard.ModeDegraded
 	default:
 		panic(fmt.Sprintf("unknown shard mode: %s", s))
 	}

pkg/local_object_storage/engine/engine.go

@@ -50,13 +50,13 @@ func (e *StorageEngine) reportShardError(
 		return
 	}
 
-	err = sh.SetMode(shard.ModeReadOnly)
+	err = sh.SetMode(shard.ModeDegraded)
 	if err != nil {
-		e.log.Error("failed to move shard in read-only mode",
+		e.log.Error("failed to move shard in degraded mode",
 			zap.Uint32("error count", errCount),
 			zap.Error(err))
 	} else {
-		e.log.Info("shard is moved in read-only due to error threshold",
+		e.log.Info("shard is moved in degraded mode due to error threshold",
 			zap.Stringer("shard_id", sh.ID()),
 			zap.Uint32("error count", errCount))
 	}

pkg/local_object_storage/engine/error_test.go

@@ -118,7 +118,7 @@ func TestErrorReporting(t *testing.T) {
 		for i := uint32(0); i < 2; i++ {
 			_, err = e.Get(&GetPrm{addr: object.AddressOf(obj)})
 			require.Error(t, err)
-			checkShardState(t, e, id[0], errThreshold+i, shard.ModeReadOnly)
+			checkShardState(t, e, id[0], errThreshold+i, shard.ModeDegraded)
 			checkShardState(t, e, id[1], 0, shard.ModeReadWrite)
 		}
 
@@ -185,7 +185,7 @@ func TestBlobstorFailback(t *testing.T) {
 		require.True(t, errors.Is(err, object.ErrRangeOutOfBounds), "got: %v", err)
 	}
 
-	checkShardState(t, e, id[0], 4, shard.ModeReadOnly)
+	checkShardState(t, e, id[0], 4, shard.ModeDegraded)
 	checkShardState(t, e, id[1], 0, shard.ModeReadWrite)
 }
 

pkg/local_object_storage/shard/delete.go

@@ -31,7 +31,7 @@ func (p *DeletePrm) WithAddresses(addr ...*addressSDK.Address) *DeletePrm {
 // Delete removes data from the shard's writeCache, metaBase and
 // blobStor.
 func (s *Shard) Delete(prm *DeletePrm) (*DeleteRes, error) {
-	if s.GetMode() == ModeReadOnly {
+	if s.GetMode() != ModeReadWrite {
 		return nil, ErrReadOnlyMode
 	}
 

pkg/local_object_storage/shard/gc.go

@@ -174,7 +174,7 @@ func (gc *gc) stop() {
 // with GC-marked graves.
 // Does nothing if shard is in "read-only" mode.
 func (s *Shard) removeGarbage() {
-	if s.GetMode() == ModeReadOnly {
+	if s.GetMode() != ModeReadWrite {
 		return
 	}
 

pkg/local_object_storage/shard/inhume.go

@@ -51,7 +51,7 @@ func (p *InhumePrm) MarkAsGarbage(addr ...*addressSDK.Address) *InhumePrm {
 //
 // Returns ErrReadOnlyMode error if shard is in "read-only" mode.
 func (s *Shard) Inhume(prm *InhumePrm) (*InhumeRes, error) {
-	if s.GetMode() == ModeReadOnly {
+	if s.GetMode() != ModeReadWrite {
 		return nil, ErrReadOnlyMode
 	}
 

pkg/local_object_storage/shard/lock.go

@@ -14,7 +14,7 @@ import (
 //
 // Locked list should be unique. Panics if it is empty.
 func (s *Shard) Lock(idCnr cid.ID, locker oid.ID, locked []oid.ID) error {
-	if s.GetMode() == ModeReadOnly {
+	if s.GetMode() != ModeReadWrite {
 		return ErrReadOnlyMode
 	}
 

pkg/local_object_storage/shard/mode.go

@@ -21,6 +21,12 @@ const (
 	// ModeReadOnly is a Mode value for shard that does not
 	// accept write operation but is readable.
 	ModeReadOnly
+
+	// ModeDegraded is a Mode value for shard that is set automatically
+	// after a certain number of errors is encountered. It is the same as
+	// `ModeReadOnly` but also enables fallback algorithms for getting object
+	// in case metabase is corrupted.
+	ModeDegraded
 )
 
 func (m Mode) String() string {
@@ -31,6 +37,8 @@ func (m Mode) String() string {
 		return "READ_WRITE"
 	case ModeReadOnly:
 		return "READ_ONLY"
+	case ModeDegraded:
+		return "DEGRADED"
 	}
 }
 
@@ -46,6 +54,8 @@ func (s *Shard) SetMode(m Mode) error {
 		switch m {
 		case ModeReadOnly:
 			s.writeCache.SetMode(writecache.ModeReadOnly)
+		case ModeDegraded:
+			s.writeCache.SetMode(writecache.ModeDegraded)
 		case ModeReadWrite:
 			s.writeCache.SetMode(writecache.ModeReadWrite)
 		}

pkg/local_object_storage/shard/move.go

@@ -27,7 +27,7 @@ func (p *ToMoveItPrm) WithAddress(addr *addressSDK.Address) *ToMoveItPrm {
 // ToMoveIt calls metabase.ToMoveIt method to mark object as relocatable to
 // another shard.
 func (s *Shard) ToMoveIt(prm *ToMoveItPrm) (*ToMoveItRes, error) {
-	if s.GetMode() == ModeReadOnly {
+	if s.GetMode() != ModeReadWrite {
 		return nil, ErrReadOnlyMode
 	}
 

pkg/local_object_storage/shard/put.go

@@ -33,7 +33,7 @@ func (p *PutPrm) WithObject(obj *object.Object) *PutPrm {
 //
 // Returns ErrReadOnlyMode error if shard is in "read-only" mode.
 func (s *Shard) Put(prm *PutPrm) (*PutRes, error) {
-	if s.GetMode() == ModeReadOnly {
+	if s.GetMode() != ModeReadWrite {
 		return nil, ErrReadOnlyMode
 	}
 

pkg/local_object_storage/writecache/delete.go

@@ -16,7 +16,7 @@ import (
 func (c *cache) Delete(addr *addressSDK.Address) error {
 	c.modeMtx.RLock()
 	defer c.modeMtx.RUnlock()
-	if c.mode == ModeReadOnly {
+	if c.readOnly() {
 		return ErrReadOnly
 	}
 

pkg/local_object_storage/writecache/flush.go

@@ -65,7 +65,7 @@ func (c *cache) flush() {
 		sz := 0
 
 		c.modeMtx.RLock()
-		if c.mode == ModeReadOnly {
+		if c.readOnly() {
 			c.modeMtx.RUnlock()
 			time.Sleep(time.Second)
 			continue
@@ -127,7 +127,7 @@ func (c *cache) flushBigObjects() {
 		select {
 		case <-tick.C:
 			c.modeMtx.RLock()
-			if c.mode == ModeReadOnly {
+			if c.readOnly() {
 				c.modeMtx.RUnlock()
 				break
 			}

pkg/local_object_storage/writecache/iterate.go

@@ -36,7 +36,7 @@ func (p *IterationPrm) WithIgnoreErrors(ignore bool) *IterationPrm {
 func (c *cache) Iterate(prm *IterationPrm) error {
 	c.modeMtx.RLock()
 	defer c.modeMtx.RUnlock()
-	if c.mode != ModeReadOnly {
+	if !c.readOnly() {
 		return nil
 	}
 

pkg/local_object_storage/writecache/mode.go

@@ -14,6 +14,9 @@ const (
 
 	// ModeReadOnly is a mode in which write-cache doesn't flush anything to a metabase.
 	ModeReadOnly
+
+	// ModeDegraded is similar to a shard's degraded mode.
+	ModeDegraded
 )
 
 // ErrReadOnly is returned when Put/Write is performed in a read-only mode.
@@ -50,3 +53,9 @@ func (c *cache) SetMode(m Mode) {
 		time.Sleep(time.Second)
 	}
 }
+
+// readOnly returns true if current mode is read-only.
+// `c.modeMtx` must be taken.
+func (c *cache) readOnly() bool {
+	return c.mode != ModeReadWrite
+}

pkg/local_object_storage/writecache/persist.go

@@ -21,7 +21,7 @@ func (c *cache) persistLoop() {
 		select {
 		case <-tick.C:
 			c.modeMtx.RLock()
-			if c.mode == ModeReadOnly {
+			if c.readOnly() {
 				c.modeMtx.RUnlock()
 				continue
 			}

pkg/local_object_storage/writecache/put.go

@@ -15,7 +15,7 @@ var ErrBigObject = errors.New("too big object")
 func (c *cache) Put(o *objectSDK.Object) error {
 	c.modeMtx.RLock()
 	defer c.modeMtx.RUnlock()
-	if c.mode == ModeReadOnly {
+	if c.readOnly() {
 		return ErrReadOnly
 	}
 

pkg/services/control/server/list_shards.go

@@ -40,6 +40,8 @@ func (s *Server) ListShards(_ context.Context, req *control.ListShardsRequest) (
 			mode = control.ShardMode_READ_WRITE
 		case shard.ModeReadOnly:
 			mode = control.ShardMode_READ_ONLY
+		case shard.ModeDegraded:
+			mode = control.ShardMode_DEGRADED
 		default:
 			mode = control.ShardMode_SHARD_MODE_UNDEFINED
 		}

pkg/services/control/server/set_shard_mode.go

@@ -29,6 +29,8 @@ func (s *Server) SetShardMode(_ context.Context, req *control.SetShardModeReques
 		mode = shard.ModeReadWrite
 	case control.ShardMode_READ_ONLY:
 		mode = shard.ModeReadOnly
+	case control.ShardMode_DEGRADED:
+		mode = shard.ModeDegraded
 	default:
 		return nil, status.Error(codes.Internal, fmt.Sprintf("unknown shard mode: %s", requestedMode))
 	}

pkg/services/control/types.proto

@@ -151,4 +151,7 @@ enum ShardMode {
 
     // Read-only.
     READ_ONLY = 2;
+
+    // Degraded.
+    DEGRADED = 3;
 }