fix(redis): namespace cache keys when no prefix is set

With an empty prefix, Clear deleted every key in the Redis database, including keys of other applications. Cache keys now start with gmp: by default. Existing cache entries become unreachable after the upgrade and expire by TTL.

cache/redis/redis.go

@@ -83,7 +83,15 @@ type RedisClientConfig struct {
 // entry.
 const defaultTTL = 60 * time.Second
 
+// DefaultKeyPrefix namespaces cache keys when no prefix is configured, so Clear
+// and CountQueries never touch keys of other applications on a shared Redis.
+const DefaultKeyPrefix = "gmp:"
+
 func New(redisClientConfig *RedisClientConfig) (*RedisConfig, error) {
+	prefix := redisClientConfig.Prefix
+	if prefix == "" {
+		prefix = DefaultKeyPrefix
+	}
 	c := &RedisConfig{
 		client: redis.NewClient(&redis.Options{
 			Addr:     redisClientConfig.RedisServer,
@@ -91,7 +99,7 @@ func New(redisClientConfig *RedisClientConfig) (*RedisConfig, error) {
 			DB:       redisClientConfig.RedisDB,
 		}),
 		ctx:    context.Background(),
-		prefix: redisClientConfig.Prefix,
+		prefix: prefix,
 		builderPool: &sync.Pool{
 			New: func() any {
 				return &strings.Builder{}