Hi team, For default broker configuration, replica.lag.max.messages is 4000 and message.max.bytes is 1Mb. In the extreme case, the follower(s) could lag by 4000 messages. The leader must save at least 4000 messages to allow follower(s) to catch up. So the minimum retention size is 4000Mb=4Gb. It is better to add this to the documentation.
In our case, message.max.bytes is much larger than 1Mb and replica.lag.max.messages is larger than 4000. This implicit minimum retention size is hundreds of Gb and we have hundreds of partitions on each broker. We feel we have to use a disk array to run Kafka. Because the topics have different maximum message size, it makes more sense to use the size gap between the leader and follower(s), e.g., say the follower(s) can only lag behind the leader by 2Gb. This makes it easier to control the behavior the brokers and save disk space. Regards, Libo
