Messages sent by a producer to a particular topic partition will be appended in the order they are sent. For example, if a message M1 and M2 are sent by the same producer, but M1 is sent first, then M1 will have a lower offset than M2 and the message M1 appears earlier in the log.

A consumer instance sees messages in the order they are stored in the log.

For a topic with replication factor N, the tolerance is up to N-1 server failures without losing any records committed to the log.