Thanks D C. Thanks a lot . That is quite a detailed explanation. If I understand correctly, ( ignoring the case where producers create transactions) - since the replica is down and never comes , the high watermark CANNOT advance and the consumer CAN NOT read the messages which were sent after the replica is down as the message is NOT committed - Hope this is correct ?
To address this situation, either we should make sure the replica is up or reduce the replication factor so that the message will be committed and consumer can start reading the messages ... Regards, Nag On Sun, Jun 21, 2020 at 3:25 AM D C <dragos.g.cri...@gmail.com> wrote: > The short answer is : yes, a consumer can only consume messages up to the > High Watermark. > > The long answer is not exactly, for the following reasons: > > At the partition level you have 3 major offsets that are important to the > health of the partition and accessibility from the consumer pov: > LeO (log end offset) - which represents the highest offset in the highest > segment > High Watermark - which represents the latest offset that has been > replicated to all the followers > LSO (Last stable offset) - which is important when you use producers that > create transactions - which represents the the highest offset that has been > committed by a transaction and that is allowed to be read with isolation > level = read_commited. > > The LeO can only be higher or equal to the High Watermark (for obvious > reasons) > The High Watermark can only be higher or equal to the LSO (the messages up > to this point may have been committed to all the followers but the > transaction isn't yet finished) > And coming to your question, in case the transaction hasn't finished, the > LSO may be lower than the High Watermark so if your consumer is accessing > the data in Read_Committed, it won't be able to surpass the LSO. > > Cheers, > D > > On Sat, Jun 20, 2020 at 9:05 PM Nag Y <andriod.nag.u...@gmail.com> wrote: > > > As I understand it, the consumer can only read "committed" messages - > which > > I believe, if we look at internals of it, committed messages are nothing > > but messages which are upto the high watermark. > > *The high watermark is the offset of the last message that was > successfully > > copied to all of the log’s replicas. * > > > > *Having said that, if one of the replica is down, will high water mark > be* > > *advanced?* > > > > *If replica can't come forever, can we consider this message cant be > > consumed by the consumer since it is never committed * > > >
