When a record is assigned an offset, that offset permanently identifies that record. The offset that identified that record will never be reused for another record.
In order to begin consuming records, a consumer must specify the topic and partition to consume from, as well as the offset into the partition where it should begin reading.
The offset of a record is its total position within its parent partition.
There are multiple ways that an offset may be derived in more convenient ways:
There is a difference between an absolute offset and a relative offset from the beginning of the partition.
When consumers specify a relative offset, the offset given by the consumer is used to calculate the actual total offset into the partition.
When a record is assigned an offset, that offset permanently identifies that record, but this does not necessarily mean that the record will always be available.
If a partition has a retention policy that causes it to begin deleting records from the beginning, then the relative-from-beginning offset will count forward from the oldest record that is still available.