From fcf53a2a787f0e1398a961fdccf877b81e97535b Mon Sep 17 00:00:00 2001
From: Vladimir Mihailenco <vladimir.webdev@gmail.com>
Date: Sun, 9 Oct 2016 08:18:57 +0000
Subject: [PATCH] Better cluster loading handling.

---
 cluster.go                | 41 ++++++++++++++++++++++++---------------
 internal/errors/errors.go |  4 +---
 2 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/cluster.go b/cluster.go
index e5011544..7689a74e 100644
--- a/cluster.go
+++ b/cluster.go
@@ -15,6 +15,11 @@ import (
 type clusterNode struct {
 	Client  *Client
 	Latency time.Duration
+	loading time.Time
+}
+
+func (n *clusterNode) Loading() bool {
+	return !n.loading.IsZero() && time.Since(n.loading) < time.Minute
 }
 
 // ClusterClient is a Redis Cluster client representing a pool of zero
@@ -218,10 +223,20 @@ func (c *ClusterClient) slotSlaveNode(slot int) (*clusterNode, error) {
 	case 1:
 		return nodes[0], nil
 	case 2:
-		return nodes[1], nil
+		if slave := nodes[1]; !slave.Loading() {
+			return slave, nil
+		}
+		return nodes[0], nil
 	default:
-		n := rand.Intn(len(nodes)-1) + 1
-		return nodes[n], nil
+		var slave *clusterNode
+		for i := 0; i < 10; i++ {
+			n := rand.Intn(len(nodes)-1) + 1
+			slave = nodes[n]
+			if !slave.Loading() {
+				break
+			}
+		}
+		return slave, nil
 	}
 }
 
@@ -287,28 +302,22 @@ func (c *ClusterClient) Process(cmd Cmder) error {
 			pipe := node.Client.Pipeline()
 			pipe.Process(NewCmd("ASKING"))
 			pipe.Process(cmd)
-			_, _ = pipe.Exec()
+			_, err = pipe.Exec()
 			pipe.Close()
 			ask = false
 		} else {
-			node.Client.Process(cmd)
+			err = node.Client.Process(cmd)
 		}
 
-		// If there is no (real) error, we are done!
-		err := cmd.Err()
+		// If there is no (real) error - we are done.
 		if err == nil {
 			return nil
 		}
 
-		// If slave is loading, read from master
-		if errors.IsLoading(cmd.Err()) && c.opt.ReadOnly {
-			trynode, err := c.slotMasterNode(slot)
-			if err == nil && trynode != node {
-				node = trynode
-				continue
-			} else {
-				break
-			}
+		// If slave is loading - read from master.
+		if c.opt.ReadOnly && errors.IsLoading(err) {
+			node.loading = time.Now()
+			continue
 		}
 
 		// On network errors try random node.
diff --git a/internal/errors/errors.go b/internal/errors/errors.go
index 49a80eae..c5abc0be 100644
--- a/internal/errors/errors.go
+++ b/internal/errors/errors.go
@@ -10,8 +10,6 @@ const Nil = RedisError("redis: nil")
 
 type RedisError string
 
-var LoadingError RedisError = "LOADING Redis is loading the dataset in memory"
-
 func (e RedisError) Error() string { return string(e) }
 
 func IsRetryable(err error) bool {
@@ -69,5 +67,5 @@ func IsMoved(err error) (moved bool, ask bool, addr string) {
 }
 
 func IsLoading(err error) bool {
-	return err.Error() == string(LoadingError)
+	return strings.HasPrefix(err.Error(), "LOADING")
 }