more code

internal/cache/cache.go

@@ -18,6 +18,7 @@ package cache
 import (
 	"encoding/binary"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"github.com/miekg/dns"
@@ -160,8 +161,11 @@ type Entry struct {
 	StaleUntil time.Time
 	// Bytes is the accounted size, used by the LRU and the size gauges.
 	Bytes int
-	// Hits counts serves since it was stored.
-	Hits uint32
+	// Hits counts serves since it was stored. It is atomic because an Entry is
+	// shared by every goroutine that hits the key (the LRU hands out the same
+	// pointer on purpose, so a hit never copies the message), and the
+	// counter is bumped outside the shard lock on the hot path.
+	Hits atomic.Uint32
 	// Neg marks a cached NXDOMAIN or NODATA answer.
 	Neg bool
 	// Truncated records that the upstream answer did not fit in 512 bytes,