a question of ISR and ack all

[XiJun Ye]

I have a question about data consistency. Kafka ISR only determines the time of 
lag, not the number of messages. Does ack=all require the replicas in the ISR 
to completely catch up with the number of messages or to meet the time 
requirement? For example, if there are 3 replicas in the ISR, 
min.insync.replicas=3 and acks=all, can the data of the 3 replicas be 
guaranteed to be completely consistent when the message is written? Instead of 
meeting the replica.lag.time.max.ms time requirement.