問題:notification system output超過fcm的rps quota limit
解法:批次發送到fcm避免峰值造成rps超過fcm quota limit
Batch & Flow Control都是能夠控制topic流量的功能
Batch :
控制publisher的send limit,在一定時間內純到N個message or size就送出,值得一提的點是幾時量沒到,時間到一樣會送出
Flow Control:
控制subscribe的receive limit,N個message(ACK or NACK)還沒處理前不會pull新message
Reference :https://medium.com/google-cloud/pub-sub-flow-control-batching-9ba9a75bce3b