Thanks James for sharing that scenario. I agree it makes sense to be able to remove offsets for the topics that are no longer "active" in the group. I think it becomes important to determine what constitutes that a topic is no longer active: If we use per-partition expiration we would manually choose a retention time that works for the particular scenario.
That works, but since we are manually intervening and specify a per-partition retention, why not do the intervention in some other way: One alternative for this intervention, to favor the simplicity of the suggested protocol in the KIP, is to improve upon the just introduced DELETE_GROUPS API and allow for deletion of offsets of specific topics in the group. This is what the old ZooKeeper based group management supported anyway, and we would just be leveling the group deletion features of the Kafka-based group management with the ZooKeeper-based one. So, instead of deciding in advance when the offsets should be removed we would instantly remove them when we are sure that they are no longer needed. Let me know what you think. Thanks. --Vahid From: James Cheng <wushuja...@gmail.com> To: dev@kafka.apache.org Date: 02/01/2018 12:37 AM Subject: Re: [DISCUSS] KIP-211: Revise Expiration Semantics of Consumer Group Offsets Vahid, Under rejected alternatives, we had decided that we did NOT want to do per-partition expiration, and instead we wait until the entire group is empty and then (after the right time has passed) expire the entire group at once. I thought of one scenario that might benefit from per-partition expiration. Let's say I have topics A B C... Z. So, I have 26 topics, all of them single partition, so 26 partitions. Let's say I have mirrormaker mirroring those 26 topics. The group will then have 26 committed offsets. Let's say I then change the whitelist on mirrormaker so that it only mirrors topic Z, but I keep the same consumer group name. (I imagine that is a common thing to do?) With the proposed design for this KIP, the committed offsets for topics A through Y will stay around as long as this mirroring group name exists. In the current implementation that already exists (prior to this KIP), I belive that committed offsets for topics A through Y will expire. How much do we care about this case? -James > On Jan 23, 2018, at 11:44 PM, Jeff Widman <j...@jeffwidman.com> wrote: > > Bumping this as I'd like to see it land... > > It's one of the "features" that tends to catch Kafka n00bs unawares and > typically results in message skippage/loss, vs the proposed solution is > much more intuitive behavior. > > Plus it's more wire efficient because consumers no longer need to commit > offsets for partitions that have no new messages just to keep those offsets > alive. > > On Fri, Jan 12, 2018 at 10:21 AM, Vahid S Hashemian < > vahidhashem...@us.ibm.com> wrote: > >> There has been no further discussion on this KIP for about two months. >> So I thought I'd provide the scoop hoping it would spark additional >> feedback and move the KIP forward. >> >> The KIP proposes a method to preserve group offsets as long as the group >> is not in Empty state (even when offsets are committed very rarely), and >> start the offset expiration of the group as soon as the group becomes >> Empty. >> It suggests dropping the `retention_time` field from the `OffsetCommit` >> request and, instead, enforcing it via the broker config >> `offsets.retention.minutes` for all groups. In other words, all groups >> will have the same retention time. >> The KIP presumes that this global retention config would suffice common >> use cases and does not lead to, e.g., unmanageable offset cache size (for >> groups that don't need to stay around that long). It suggests opening >> another KIP if this global retention setting proves to be problematic in >> the future. It was suggested earlier in the discussion thread that the KIP >> should propose a per-group retention config to circumvent this risk. >> >> I look forward to hearing your thoughts. Thanks! >> >> --Vahid >> >> >> >> >> From: "Vahid S Hashemian" <vahidhashem...@us.ibm.com> >> To: dev <dev@kafka.apache.org> >> Date: 10/18/2017 04:45 PM >> Subject: [DISCUSS] KIP-211: Revise Expiration Semantics of Consumer >> Group Offsets >> >> >> >> Hi all, >> >> I created a KIP to address the group offset expiration issue reported in >> KAFKA-4682: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__cwiki. >> apache.org_confluence_display_KAFKA_KIP-2D211-253A-2BRevise- >> 2BExpiration-2BSemantics-2Bof-2BConsumer-2BGroup-2BOffsets& >> d=DwIFAg&c=jf_iaSHvJObTbx-siA1ZOg&r=Q_itwloTQj3_xUKl7Nzswo6KE4Nj- >> kjJc7uSVcviKUc&m=JkzH_2jfSMhCUPMk3rUasrjDAId6xbAEmX7_shSYdU4&s= >> UBu7D2Obulg0fterYxL5m8xrDWkF_O2kGlygTCWsfFc&e= >> >> >> Your feedback is welcome! >> >> Thanks. >> --Vahid >> >> >> >> >> >> > > > -- > > *Jeff Widman* > jeffwidman.com < https://urldefense.proofpoint.com/v2/url?u=http-3A__www.jeffwidman.com_&d=DwIFAg&c=jf_iaSHvJObTbx-siA1ZOg&r=Q_itwloTQj3_xUKl7Nzswo6KE4Nj-kjJc7uSVcviKUc&m=TpGQEOVxEJ-3Y4rXTBP5CW7iUmO3PYKt_WeEDomWkAs&s=WXmFA_R-gtKbl9KgDfhHB4flnaBUB5C0ypRy4n9xkoI&e= > | 740-WIDMAN-J (943-6265) > <><
