From 2b111081f20d534208e6525f83abc5766b677995 Mon Sep 17 00:00:00 2001
From: srikar-jilugu <srikar.jilugu@zomato.com>
Date: Fri, 5 Jul 2024 13:43:49 +0530
Subject: [PATCH 1/2] fix node routing when all nodes are failing

---
 osscluster.go | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/osscluster.go b/osscluster.go
index e28cb1e39..40f5bd110 100644
--- a/osscluster.go
+++ b/osscluster.go
@@ -341,6 +341,8 @@ func (n *clusterNode) Close() error {
 	return n.Client.Close()
 }
 
+const maximumNodeLatency = 1 * time.Minute
+
 func (n *clusterNode) updateLatency() {
 	const numProbe = 10
 	var dur uint64
@@ -361,7 +363,7 @@ func (n *clusterNode) updateLatency() {
 	if successes == 0 {
 		// If none of the pings worked, set latency to some arbitrarily high value so this node gets
 		// least priority.
-		latency = float64((1 * time.Minute) / time.Microsecond)
+		latency = float64((maximumNodeLatency) / time.Microsecond)
 	} else {
 		latency = float64(dur) / float64(successes)
 	}
@@ -735,21 +737,39 @@ func (c *clusterState) slotClosestNode(slot int) (*clusterNode, error) {
 		return c.nodes.Random()
 	}
 
-	var node *clusterNode
+	var allNodesFailing = true
+	var (
+		closestNonFailingNode *clusterNode
+		closestNode           *clusterNode
+		minLatency            time.Duration
+	)
+
 	for _, n := range nodes {
-		if n.Failing() {
-			continue
-		}
-		if node == nil || n.Latency() < node.Latency() {
-			node = n
+		if closestNode == nil || n.Latency() < minLatency {
+			closestNode = n
+			minLatency = n.Latency()
+			if !n.Failing() {
+				closestNonFailingNode = n
+				allNodesFailing = false
+			}
 		}
 	}
-	if node != nil {
-		return node, nil
+
+	// pick the healthly node with the lowest latency
+	if !allNodesFailing && closestNonFailingNode != nil {
+		return closestNonFailingNode, nil
 	}
 
-	// If all nodes are failing - return random node
-	return c.nodes.Random()
+	// if all nodes are failing, we will pick the temporarily failing node with lowest latency
+	if minLatency < maximumNodeLatency {
+		internal.Logger.Printf(context.TODO(), "redis: all nodes are failing, picking the temporarily failing node with lowest latency")
+		return closestNode, nil
+	}
+
+	// If all nodes are having the maximum latency(all pings are failing) - return a random node within the nodes corresponding to the slot
+	randomNodes := rand.Perm(len(nodes))
+	internal.Logger.Printf(context.TODO(), "redis: pings to all nodes are failing, picking a random node within the slot")
+	return nodes[randomNodes[0]], nil
 }
 
 func (c *clusterState) slotRandomNode(slot int) (*clusterNode, error) {

From 34c1db18c2346c9776cdd3fa778916663b5ecfc8 Mon Sep 17 00:00:00 2001
From: srikar-jilugu <srikar.jilugu@zomato.com>
Date: Mon, 8 Jul 2024 19:17:28 +0530
Subject: [PATCH 2/2] fix minlatency zero value

---
 osscluster.go | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/osscluster.go b/osscluster.go
index 40f5bd110..73a9e2b74 100644
--- a/osscluster.go
+++ b/osscluster.go
@@ -744,6 +744,9 @@ func (c *clusterState) slotClosestNode(slot int) (*clusterNode, error) {
 		minLatency            time.Duration
 	)
 
+	// setting the max possible duration as zerovalue for minlatency
+	minLatency = time.Duration(math.MaxInt64)
+
 	for _, n := range nodes {
 		if closestNode == nil || n.Latency() < minLatency {
 			closestNode = n
@@ -761,15 +764,14 @@ func (c *clusterState) slotClosestNode(slot int) (*clusterNode, error) {
 	}
 
 	// if all nodes are failing, we will pick the temporarily failing node with lowest latency
-	if minLatency < maximumNodeLatency {
-		internal.Logger.Printf(context.TODO(), "redis: all nodes are failing, picking the temporarily failing node with lowest latency")
+	if minLatency < maximumNodeLatency && closestNode != nil {
+		internal.Logger.Printf(context.TODO(), "redis: all nodes are marked as failed, picking the temporarily failing node with lowest latency")
 		return closestNode, nil
 	}
 
-	// If all nodes are having the maximum latency(all pings are failing) - return a random node within the nodes corresponding to the slot
-	randomNodes := rand.Perm(len(nodes))
-	internal.Logger.Printf(context.TODO(), "redis: pings to all nodes are failing, picking a random node within the slot")
-	return nodes[randomNodes[0]], nil
+	// If all nodes are having the maximum latency(all pings are failing) - return a random node across the cluster
+	internal.Logger.Printf(context.TODO(), "redis: pings to all nodes are failing, picking a random node across the cluster")
+	return c.nodes.Random()
 }
 
 func (c *clusterState) slotRandomNode(slot int) (*clusterNode, error) {