hrpc: add an option to skip retry

This let the caller tell GoHBase to no retry calls that failed.
Otherwise, GoHBase will retry forever until cancellation of the context.
But sometime, it is useful to to be able to say "try only once", without
just relying on having a small context timeout.

One of the place where this is useful is when we try to close a scanner
that we prematurely stopped, as this is just the client trying to be a
good citizen. But most likely, if the request failed with a retryable
error (region closed or moved, call queue too big, etc), by the time we
manage to send the request the scanner lease would have been already
expired on HBase side.

hrpc/call.go

@@ -61,6 +61,7 @@ type Call interface {
 	ResultChan() chan RPCResult
 	Description() string // Used for tracing and metrics
 	Context() context.Context
+	SkipRetry() bool
 }
 
 type withOptions interface {
@@ -90,6 +91,20 @@ func SkipBatch() func(Call) error {
 	}
 }
 
+func SkipRetry() func(Call) error {
+	return func(c Call) error {
+		if b, ok := c.(canSetSkipRetry); ok {
+			b.setSkipRetry(true)
+			return nil
+		}
+		return errors.New("'SkipRetry' is not implemented for this call")
+	}
+}
+
+type canSetSkipRetry interface {
+	setSkipRetry(v bool)
+}
+
 // hasQueryOptions is interface that needs to be implemented by calls
 // that allow to provide Families and Filters options.
 type hasQueryOptions interface {
@@ -119,12 +134,22 @@ type base struct {
 
 	region   RegionInfo
 	resultch chan RPCResult
+
+	skipRetry bool
 }
 
 func (b *base) Context() context.Context {
 	return b.ctx
 }
 
+func (b *base) SkipRetry() bool {
+	return b.skipRetry
+}
+
+func (b *base) setSkipRetry() {
+	b.skipRetry = true
+}
+
 func (b *base) Region() RegionInfo {
 	return b.region
 }

region/multi.go

@@ -323,6 +323,11 @@ func (m *multi) Context() context.Context {
 	return context.Background()
 }
 
+// SkipRetry always returns false for Multi.
+func (m *multi) SkipRetry() bool {
+	return false
+}
+
 // String returns a description of this call
 func (m *multi) String() string {
 	return "MULTI"

rpc.go

@@ -97,16 +97,18 @@ func (c *client) SendRPC(rpc hrpc.Call) (msg proto.Message, err error) {
 			return nil, err
 		}
 		msg, err = c.sendRPCToRegionClient(ctx, rpc, rc)
-		switch err.(type) {
-		case region.RetryableError:
-			sp.AddEvent("retrySleep")
-			backoff, err = sleepAndIncreaseBackoff(ctx, backoff)
-			if err != nil {
-				return msg, err
+		if !rpc.SkipRetry() {
+			switch err.(type) {
+			case region.RetryableError:
+				sp.AddEvent("retrySleep")
+				backoff, err = sleepAndIncreaseBackoff(ctx, backoff)
+				if err != nil {
+					return msg, err
+				}
+				continue // retry
+			case region.ServerError, region.NotServingRegionError:
+				continue // retry
 			}
-			continue // retry
-		case region.ServerError, region.NotServingRegionError:
-			continue // retry
 		}
 		return msg, err
 	}

rpc_test.go

@@ -88,6 +88,7 @@ func TestSendRPCSanity(t *testing.T) {
 	expMsg := &pb.ScanResponse{}
 	result <- hrpc.RPCResult{Msg: expMsg}
 	mockCall.EXPECT().ResultChan().Return(result).Times(1)
+	mockCall.EXPECT().SkipRetry().Return(false)
 	msg, err := c.SendRPC(mockCall)
 	if err != nil {
 		t.Fatal(err)

scanner.go

@@ -337,22 +337,20 @@ func (s *scanner) closeRegionScanner() {
 		return
 	}
 	if !s.rpc.IsClosing() {
-		// Not closed at server side
-		// if we are closing in the middle of scanning a region,
-		// send a close scanner request
-		// TODO: add a deadline
+		// Not closed at server side if we are closing in the middle of scanning
+		// a region, so send a close scanner request. This is a fire-and-forget
+		// call, as if we fail the scanner lease will expire and be closed
+		// automatically by HBase.
 		rpc, err := hrpc.NewScanRange(context.Background(),
 			s.rpc.Table(), s.startRow, nil,
 			hrpc.ScannerID(s.curRegionScannerID),
 			hrpc.CloseScanner(),
-			hrpc.NumberOfRows(0))
+			hrpc.NumberOfRows(0),
+			hrpc.SkipRetry(),
+		)
 		if err != nil {
 			panic(fmt.Sprintf("should not happen: %s", err))
 		}
-
-		// If the request fails, the scanner lease will be expired
-		// and it will be closed automatically by hbase.
-		// No need to bother clients about that.
 		go s.SendRPC(rpc)
 	}
 	s.curRegionScannerID = noScannerID