Only check latencies once every 10 seconds with routeByLatency

`routeByLatency` currently checks latencies any time a server returns
a MOVED or READONLY reply. When a shard is down, the ClusterClient
chooses to issue the request to a random server, which returns a MOVED
reply. This causes a state refresh and a latency update on all servers.
This can lead to significant ping load to clusters with a large number
of clients.

This introduces logic to ping only once every 10 seconds, only
performing a latency update on a node during the `GC` function if the
latency was set later than 10 seconds ago.

Fixes #2782

Author: justinmir

osscluster.go

@@ -21,6 +21,10 @@ import (
 	"github.com/redis/go-redis/v9/internal/rand"
 )
 
+const (
+	minLatencyMeasurementInterval = 10 * time.Second
+)
+
 var errClusterNoNodes = fmt.Errorf("redis: cluster has no nodes")
 
 // ClusterOptions are used to configure a cluster client and should be
@@ -309,6 +313,8 @@ type clusterNode struct {
 	latency    uint32 // atomic
 	generation uint32 // atomic
 	failing    uint32 // atomic
+
+	lastLatencyMeasurement int64
 }
 
 func newClusterNode(clOpt *ClusterOptions, addr string) *clusterNode {
@@ -359,6 +365,7 @@ func (n *clusterNode) updateLatency() {
 		latency = float64(dur) / float64(successes)
 	}
 	atomic.StoreUint32(&n.latency, uint32(latency+0.5))
+	n.SetLastLatencyMeasurement(time.Now())
 }
 
 func (n *clusterNode) Latency() time.Duration {
@@ -388,6 +395,10 @@ func (n *clusterNode) Generation() uint32 {
 	return atomic.LoadUint32(&n.generation)
 }
 
+func (n *clusterNode) LastLatencyMeasurement() int64 {
+	return atomic.LoadInt64(&n.lastLatencyMeasurement)
+}
+
 func (n *clusterNode) SetGeneration(gen uint32) {
 	for {
 		v := atomic.LoadUint32(&n.generation)
@@ -397,6 +408,15 @@ func (n *clusterNode) SetGeneration(gen uint32) {
 	}
 }
 
+func (n *clusterNode) SetLastLatencyMeasurement(t time.Time) {
+	for {
+		v := atomic.LoadInt64(&n.lastLatencyMeasurement)
+		if t.Unix() < v || atomic.CompareAndSwapInt64(&n.lastLatencyMeasurement, v, t.Unix()) {
+			break
+		}
+	}
+}
+
 //------------------------------------------------------------------------------
 
 type clusterNodes struct {
@@ -484,10 +504,11 @@ func (c *clusterNodes) GC(generation uint32) {
 	c.mu.Lock()
 
 	c.activeAddrs = c.activeAddrs[:0]
+	now := time.Now()
 	for addr, node := range c.nodes {
 		if node.Generation() >= generation {
 			c.activeAddrs = append(c.activeAddrs, addr)
-			if c.opt.RouteByLatency {
+			if c.opt.RouteByLatency && node.LastLatencyMeasurement() < now.Add(-minLatencyMeasurementInterval).Unix() {
 				go node.updateLatency()
 			}
 			continue