From 1ec5f3ba1c8c65310d2322b62172a5510a5a72a8 Mon Sep 17 00:00:00 2001
From: Austen McClernon <austen@cockroachlabs.com>
Date: Mon, 19 Aug 2024 17:35:11 +0000
Subject: [PATCH 1/2] kvcoord: safe format replica slice

Introduce a `SafeFormat` method on `ReplicaSlice`, which can be used to
print out the replica slice in logging.

Informs: #129031
Release note: None
---
 pkg/kv/kvclient/kvcoord/BUILD.bazel      |  1 +
 pkg/kv/kvclient/kvcoord/replica_slice.go | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/pkg/kv/kvclient/kvcoord/BUILD.bazel b/pkg/kv/kvclient/kvcoord/BUILD.bazel
index ca63215d9630..12ce56996eb5 100644
--- a/pkg/kv/kvclient/kvcoord/BUILD.bazel
+++ b/pkg/kv/kvclient/kvcoord/BUILD.bazel
@@ -71,6 +71,7 @@ go_library(
         "//pkg/util/future",
         "//pkg/util/grpcutil",
         "//pkg/util/hlc",
+        "//pkg/util/humanizeutil",
         "//pkg/util/iterutil",
         "//pkg/util/limit",
         "//pkg/util/log",
diff --git a/pkg/kv/kvclient/kvcoord/replica_slice.go b/pkg/kv/kvclient/kvcoord/replica_slice.go
index dcbfda6ec6d1..8fc8445f2a13 100644
--- a/pkg/kv/kvclient/kvcoord/replica_slice.go
+++ b/pkg/kv/kvclient/kvcoord/replica_slice.go
@@ -19,9 +19,11 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/kv/kvclient"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
+	"github.com/cockroachdb/cockroach/pkg/util/humanizeutil"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/shuffle"
 	"github.com/cockroachdb/errors"
+	"github.com/cockroachdb/redact"
 )
 
 // ReplicaInfo extends the Replica structure with the associated node
@@ -41,6 +43,25 @@ type ReplicaInfo struct {
 // A ReplicaSlice is a slice of ReplicaInfo.
 type ReplicaSlice []ReplicaInfo
 
+func (rs ReplicaSlice) String() string {
+	return redact.StringWithoutMarkers(rs)
+}
+
+// SafeFormat implements the redact.SafeFormatter interface.
+func (rs ReplicaSlice) SafeFormat(w redact.SafePrinter, _ rune) {
+	var buf redact.StringBuilder
+	buf.Print("[")
+	for i, r := range rs {
+		if i > 0 {
+			buf.Print(",")
+		}
+		buf.Printf("%v(health=%v match=%d latency=%v)",
+			r, r.healthy, r.tierMatchLength, humanizeutil.Duration(r.latency))
+	}
+	buf.Print("]")
+	w.Print(buf)
+}
+
 // ReplicaSliceFilter controls which kinds of replicas are to be included in
 // the slice for routing BatchRequests to.
 type ReplicaSliceFilter int

From d2817637ea68010e5e744533195b2001f5910b9e Mon Sep 17 00:00:00 2001
From: Austen McClernon <austen@cockroachlabs.com>
Date: Mon, 19 Aug 2024 17:42:25 +0000
Subject: [PATCH 2/2] kvcoord: log replica order on nearest routing policy

Previously, we would log an event when routing to the nearest replica,
which would then show up in traces and could be used to determine the
routing policy of a query.

It is also useful to know how the nearest replica was selected i.e.,
latency, locality or by health. Log the event after sorting by the
replicas' distance to the sender and include the replica order.

Informs: #129031
Release note: None
---
 pkg/kv/kvclient/kvcoord/dist_sender.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkg/kv/kvclient/kvcoord/dist_sender.go b/pkg/kv/kvclient/kvcoord/dist_sender.go
index 35526165c8a4..59242b1bc12c 100644
--- a/pkg/kv/kvclient/kvcoord/dist_sender.go
+++ b/pkg/kv/kvclient/kvcoord/dist_sender.go
@@ -2571,8 +2571,8 @@ func (ds *DistSender) sendToReplicas(
 
 	case kvpb.RoutingPolicy_NEAREST:
 		// Order by latency.
-		log.VEvent(ctx, 2, "routing to nearest replica; leaseholder not required")
 		replicas.OptimizeReplicaOrder(ds.st, ds.nodeIDGetter(), ds.healthFunc, ds.latencyFunc, ds.locality)
+		log.VEventf(ctx, 2, "routing to nearest replica; leaseholder not required order=%v", replicas)
 
 	default:
 		log.Fatalf(ctx, "unknown routing policy: %s", ba.RoutingPolicy)