fix(cmdSlot): Add preferred random slot

Author: ndyakov

internal_test.go

@@ -364,15 +364,22 @@ var _ = Describe("ClusterClient", func() {
 		It("select slot from args for GETKEYSINSLOT command", func() {
 			cmd := NewStringSliceCmd(ctx, "cluster", "getkeysinslot", 100, 200)
 
-			slot := client.cmdSlot(cmd)
+			slot := client.cmdSlot(cmd, -1)
 			Expect(slot).To(Equal(100))
 		})
 
 		It("select slot from args for COUNTKEYSINSLOT command", func() {
 			cmd := NewStringSliceCmd(ctx, "cluster", "countkeysinslot", 100)
 
-			slot := client.cmdSlot(cmd)
+			slot := client.cmdSlot(cmd, -1)
 			Expect(slot).To(Equal(100))
 		})
+
+		It("follows preferred random slot", func() {
+			cmd := NewStatusCmd(ctx, "ping")
+
+			slot := client.cmdSlot(cmd, 101)
+			Expect(slot).To(Equal(101))
+		})
 	})
 })

osscluster.go

@@ -998,7 +998,7 @@ func (c *ClusterClient) Process(ctx context.Context, cmd Cmder) error {
 }
 
 func (c *ClusterClient) process(ctx context.Context, cmd Cmder) error {
-	slot := c.cmdSlot(cmd)
+	slot := c.cmdSlot(cmd, -1)
 	var node *clusterNode
 	var moved bool
 	var ask bool
@@ -1344,9 +1344,13 @@ func (c *ClusterClient) mapCmdsByNode(ctx context.Context, cmdsMap *cmdsMap, cmd
 		return err
 	}
 
+	preferredRandomSlot := -1
 	if c.opt.ReadOnly && c.cmdsAreReadOnly(ctx, cmds) {
 		for _, cmd := range cmds {
-			slot := c.cmdSlot(cmd)
+			slot := c.cmdSlot(cmd, preferredRandomSlot)
+			if preferredRandomSlot == -1 {
+				preferredRandomSlot = slot
+			}
 			node, err := c.slotReadOnlyNode(state, slot)
 			if err != nil {
 				return err
@@ -1357,7 +1361,10 @@ func (c *ClusterClient) mapCmdsByNode(ctx context.Context, cmdsMap *cmdsMap, cmd
 	}
 
 	for _, cmd := range cmds {
-		slot := c.cmdSlot(cmd)
+		slot := c.cmdSlot(cmd, preferredRandomSlot)
+		if preferredRandomSlot == -1 {
+			preferredRandomSlot = slot
+		}
 		node, err := state.slotMasterNode(slot)
 		if err != nil {
 			return err
@@ -1594,8 +1601,12 @@ func (c *ClusterClient) processTxPipeline(ctx context.Context, cmds []Cmder) err
 
 func (c *ClusterClient) mapCmdsBySlot(cmds []Cmder) map[int][]Cmder {
 	cmdsMap := make(map[int][]Cmder)
+	preferredRandomSlot := -1
 	for _, cmd := range cmds {
-		slot := c.cmdSlot(cmd)
+		slot := c.cmdSlot(cmd, preferredRandomSlot)
+		if preferredRandomSlot == -1 {
+			preferredRandomSlot = slot
+		}
 		cmdsMap[slot] = append(cmdsMap[slot], cmd)
 	}
 	return cmdsMap
@@ -1925,17 +1936,20 @@ func (c *ClusterClient) cmdInfo(ctx context.Context, name string) *CommandInfo {
 	return info
 }
 
-func (c *ClusterClient) cmdSlot(cmd Cmder) int {
+func (c *ClusterClient) cmdSlot(cmd Cmder, preferredRandomSlot int) int {
 	args := cmd.Args()
 	if args[0] == "cluster" && (args[1] == "getkeysinslot" || args[1] == "countkeysinslot") {
 		return args[2].(int)
 	}
 
-	return cmdSlot(cmd, cmdFirstKeyPos(cmd))
+	return cmdSlot(cmd, cmdFirstKeyPos(cmd), preferredRandomSlot)
 }
 
-func cmdSlot(cmd Cmder, pos int) int {
+func cmdSlot(cmd Cmder, pos int, preferredRandomSlot int) int {
 	if pos == 0 {
+		if preferredRandomSlot != -1 {
+			return preferredRandomSlot
+		}
 		return hashtag.RandomSlot()
 	}
 	firstKey := cmd.stringArg(pos)