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Kafka >> mail # user >> Handling consumer rebalance when implementing synchronous auto-offset commit


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Re: Handling consumer rebalance when implementing synchronous auto-offset commit
That would be great.  Additionally, in the new api, it would be awesome
augment the default auto-commit functionality to allow client code to mark
a message for commit only after processing a message successfully!
On Wed, Oct 16, 2013 at 7:52 AM, Jun Rao <[EMAIL PROTECTED]> wrote:

> 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>
> > 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