理解 RUM 采样：机制、规则与最佳实践

val prefs = getSharedPreferences("rum_config", Context.MODE_PRIVATE)

// 1. 用本地缓存的值立即初始化，不阻塞 SDK 启动
val sampleRate = prefs.getFloat("session_sample_rate", 20f)

val rumConfig = RumConfiguration.Builder(applicationId)
    .setSessionSampleRate(sampleRate)
    .build()
Rum.enable(rumConfig)

// 2. 异步拉取最新值写入缓存，下次冷启动生效
CoroutineScope(Dispatchers.IO).launch {
    runCatching { fetchRumConfig() } // 请求您自己的配置服务
        .onSuccess { config ->
            prefs.edit()
                .putFloat("session_sample_rate", config.sessionSampleRate)
                .apply()
        } // 拉取失败时沿用缓存值，不影响采集
}

let defaults = UserDefaults.standard

// 1. 用本地缓存的值立即初始化，不阻塞 SDK 启动
let sampleRate = defaults.object(forKey: "rumSessionSampleRate") as? Float ?? 20

var rumConfig = RUM.Configuration(applicationID: "<RUM_APPLICATION_ID>")
rumConfig.sessionSampleRate = sampleRate
RUM.enable(with: rumConfig)

// 2. 异步拉取最新值写入缓存，下次冷启动生效
URLSession.shared.dataTask(with: configURL) { data, _, _ in
    guard let data,
          let config = try? JSONDecoder().decode(RumRemoteConfig.self, from: data)
    else { return } // 拉取失败时沿用缓存值，不影响采集
    defaults.set(config.sessionSampleRate, forKey: "rumSessionSampleRate")
}.resume()

// 拉取到新配置时只记录待生效值，不立刻重建
func onConfigFetched(_ latest: RumRemoteConfig) {
    defaults.set(latest.sessionSampleRate, forKey: "rumSessionSampleRate")
    pendingSampleRate = latest.sessionSampleRate != currentSampleRate
        ? latest.sessionSampleRate : nil
}

// App 回前台这类安静时机再执行重建
NotificationCenter.default.addObserver(
    forName: UIApplication.willEnterForegroundNotification, object: nil, queue: .main
) { _ in
    guard let newRate = pendingSampleRate else { return }
    pendingSampleRate = nil

    Datadog.stopInstance() // 停止当前实例
    Datadog.initialize(with: coreConfiguration, trackingConsent: .granted)
    var rumConfig = RUM.Configuration(applicationID: "<RUM_APPLICATION_ID>")
    rumConfig.sessionSampleRate = newRate
    RUM.enable(with: rumConfig) // 启用过的其他产品（Logs、Trace 等）也要一并重新 enable
    currentSampleRate = newRate
}

fun decideSampling(user: User, config: RumRemoteConfig): Boolean {
    // 优先级从高到低的短路规则
    if (config.incidentMode) return true            // 故障排查模式：全量采集
    if (user.isInternal || user.isBeta) return true // 内部/灰度用户：必采
    if (user.isVip) return true                     // 重点用户：必采
    if (prefs.getBoolean("rum_had_error", false)) return true // 上次出过错：必采

    // 底座：按 userId 确定性哈希分桶
    return hash(user.id + config.salt) % 100 < config.sampleRate
}

val sampled = decideSampling(currentUser, cachedConfig)

val rumConfig = RumConfiguration.Builder(applicationId)
    .setSessionSampleRate(if (sampled) 100f else 0f)
    .build()
Rum.enable(rumConfig)

func decideSampling(user: User, config: RumRemoteConfig) -> Bool {
    // 优先级从高到低的短路规则
    if config.incidentMode { return true }            // 故障排查模式：全量采集
    if user.isInternal || user.isBeta { return true } // 内部/灰度用户：必采
    if user.isVip { return true }                     // 重点用户：必采
    if UserDefaults.standard.bool(forKey: "rumHadError") { return true } // 上次出过错：必采

    // 底座：按 userId 确定性哈希分桶
    return hash(user.id + config.salt) % 100 < config.sampleRate
}

let sampled = decideSampling(user: currentUser, config: cachedConfig)

var rumConfig = RUM.Configuration(applicationID: "<RUM_APPLICATION_ID>")
rumConfig.sessionSampleRate = sampled ? 100 : 0
RUM.enable(with: rumConfig)