Hi Jun, I ran into the same question today (see thread, subject: Consumer / Streams causes deletes in __consumer_offsets?), and here's what Eno and Guozhang helped me understand:
There are broker-level configuration values called "offsets.retention.minutes" and "offsets.retention.check.interval.ms". Every "offsets.retention.check.interval.ms", consumer group offsets that haven't been published in "offsets.retention.minutes" have a null record published in the __consumer_offsets topic, so that the eventual compaction of the topic will clean them up. :-) Mathieu On Wed, Feb 22, 2017 at 6:59 PM, Jun MA <mj.saber1...@gmail.com> wrote: > Hi Todd, > > Thank you so much for your reply. I assume that the broker will produce > the tombstone to __consumer_offsets topic when the offset expires? I’m > curious how broker notices the offset expires? Does it store the offset > message in memory and periodically check if someone expires? > > Thanks, > Jun > > > On Feb 22, 2017, at 4:37 PM, Todd Palino <tpal...@gmail.com> wrote: > > > > __consumer_offsets is a log-compacted topic, and a NULL body indicates a > > delete tombstone. So it means to delete the entry that matches the key > > (group, topic, partition tuple). > > > > -Todd > > > > > > > > On Wed, Feb 22, 2017 at 3:50 PM, Jun MA <mj.saber1...@gmail.com> wrote: > > > >> Hi guys, > >> > >> I’m trying to consume from __consumer_offsets topic to get exact > committed > >> offset of each consumer. Normally I can see messages like: > >> > >> [eds-els-recopp-jenkins-01-5651,eds-incre-staging-1,0]::[ > >> OffsetMetadata[29791925,NO_METADATA],CommitTime > >> 1487090167367,ExpirationTime 1487176567367], > >> > >> which make sense to me. But sometimes I see messages like: > >> > >> [eds-elssearchindex-curiosity-stg-10892,eds-incre-v2-staging > -els,0]::NULL. > >> > >> Can someone explains what is NULL means here and why a NULL value get > >> published to __consumer_offsets? > >> > >> We’re running kafka 0.9.0.1 and we use org.apache.kafka.common. > >> serialization.ByteArrayDeserializer and GroupMetadataManager.OffsetsMe > ssageFormatter > >> to parse the message. > >> > >> Thanks, > >> Jun > > > > > > > > > > -- > > *Todd Palino* > > Staff Site Reliability Engineer > > Data Infrastructure Streaming > > > > > > > > linkedin.com/in/toddpalino > >
