Hi, Jiunn-Yang and Chia-Ping, Thanks for the reply.
"The core semantic of to_start_time is to read all records since the creation of the group." I am just questioning whether this actually covers a common use case. If the offset doesn't go out of range, the logic makes sense to me. I'm not sure about the logic if the offset is out of range. If a user chooses to skip the historical data when starting the group, it seems the user likely wants to do the same if the offset is out of range. Jun On Fri, Apr 17, 2026 at 5:23 AM 黃竣陽 <[email protected]> wrote: > Hello Jun, > > Thank for the feedback, > > Adding to the points above: > > Regarding by_duration as an alternative to Scenario 1: beyond clock skew > and retry issues, there is also a usability concern. by_duration requires > users > to reason about operational timing — "how long does partition discovery > take > in my environment?”, and then translate that into a configuration value. > to_start_time > requires no such reasoning. It simply anchors to the group creation time > recorded > by the broker. > > Regarding Scenario 2: I'd also like to clarify that to_start_time does not > branch between > "use latest" and "use earliest." It applies the same ListOffsetsRequest > with the group creation > timestamp in all cases. The difference in outcome: > - skipping old data on first start > - consuming surviving data after truncation > is a natural consequence of what data exists in the partition at that > point, not a different policy > being applied. The rule is always the same. > > Best Regards, > Jiunn-Yang > > > Chia-Ping Tsai <[email protected]> 於 2026年4月17日 上午9:48 寫道： > > > > > >> Jun Rao via dev <[email protected]> 於 2026年4月17日 凌晨4:57 寫道： > >> > >> Also, a group is deleted after the consumer has been idle longer > >> than offsets.retention.minutes. What's the semantic of to_start_time if > the > >> group creation time is unavailable? > > > > If the group is recreated, a new creation time will be recorded. Hence, > it acts like a new group. Plus, it throws an exception directly if the > group truly has no creation time. > >
