For manual offset commits, it will be useful to have some kind of API that informs the client when a rebalance is going to happen. We can think about this when we do the client rewrite.
Thanks, Jun On Tue, Oct 15, 2013 at 9:21 PM, Jason Rosenberg <j...@squareup.com> wrote: > Jun, > > Yes, sorry, I think that was the basis for my question. When auto commit > is enabled, special care is taken to make sure things are auto-committed > during a rebalance. This is needed because when a topic moves off of a > consumer thread (since it is being rebalanced to another one), it's as if > that topic is being shutdown on that connector, and any not-yet-committed > messages need to be committed before letting go of the topic. > > So, my question is around trying to understand if there's a way I can > reproduce similar functionality using my own sync auto commit > implementation (and I'm not sure there is). It seems that when there's a > rebalance, all processed but not-yet-committed offsets will not be > committed, and thus there will be no way to prevent pretty massive > duplicate consumption on a rebalance. Is that about right? Or is there > someway around this that I'm not seeing? > > The auto-commit functionality that's builtin is so close to being all that > anyone would need, except it has a glaring weakness, in that it will cause > messages to be lost from time to time, and so I don't know that it will > meet the needs of trying to have reliable delivery (with duplicates ok). > > Jason > > > On Tue, Oct 15, 2013 at 9:00 PM, Jun Rao <jun...@gmail.com> wrote: > > > If auto commit is disabled, the consumer connector won't call > commitOffsets > > during rebalancing. > > > > Thanks, > > > > Jun > > > > > > On Tue, Oct 15, 2013 at 4:16 PM, Jason Rosenberg <j...@squareup.com> > wrote: > > > > > I'm looking at implementing a synchronous auto offset commit solution. > > > People have discussed the need for this in previous > > > threads......Basically, in my consumer loop, I want to make sure a > > message > > > has been actually processed before allowing it's offset to be > committed. > > > But I don't want to commit on every message, since that would be too > > > expensive. So, I want to use the 'auto.commit.interval.ms' to > > > periodically > > > call commitOffsets, but only after a message is processed, but not > after > > > the next message has been issued via a call to 'next()' on the > > > ConsumerIterator. > > > > > > The builtin 'auto.commit.enable' feature unfortunately allows commits > to > > > happen on any message that has been returned via > ConsumerIterator.next(). > > > But if the consumer goes down before actually processing the message, > or > > > if it hangs indefinitely for some reason, then this message will get > > > committed before it has actually been consumed successfully. > > > > > > I think there are issues with trying to implement this on top of the > > > high-level consumer api. First, I need to worry about multiple threads > > > consuming in the same connector (so for now I'm limiting this to > support > > > only 1 thread). > > > > > > Also, when shutting down the connector, I need to make sure any pending > > > messages are committed before allowing the connector to shutdown. So, > > that > > > seems easy enough to handle. > > > > > > One thing I'm more concerned with, is what happens when there's a > > consumer > > > rebalance. Looking at the ZookeeperConsumerConnector code, it seems > > there > > > are explicit calls to commitOffsets during the rebalance. I'm not sure > > how > > > to handle that from the high-level api (and do I need to worry about > > > that?). > > > > > > Thanks for any insight. > > > > > > Jason > > > > > >
