What is the default log retention period in Kafka?

The default retention period is 7 days. At the broker level it comes from log.retention.hours, default 168; log.retention.minutes and log.retention.ms, if set, take precedence in that order (log.retention.ms defaults to null, so it is not what sets the 7 days). Per topic it can be overridden with retention.ms, whose default is 604800000 (7 days); -1 means no time limit. Size-based retention is off by default: retention.bytes (and log.retention.bytes) default to -1. Deletion happens one log segment at a time, and for time-based retention the largest timestamp in a segment decides the retention time of the whole segment, so a segment is only deleted once its newest record is past retention. If both time and size limits are set, a segment eligible under either one is deleted.

Expected key concepts: 7 days, 168, log.retention.hours, log.retention.ms, 604800000, retention.ms, retention.bytes, segment, largest timestamp