Hello Jiang,
That is a valid point. The reason we design ack=-1 to be "receive acks from
replicas in ISR" is basically trading consistency for availability. I think
instead of change it meaning, we could add another ack, -2 for instance, to
specify "receive acks from all replicas" as a favor of consistency.
Since you already did this much investigation would you like to file a JIRA
and submit a patch for this?
Guozhang
On Fri, Jul 11, 2014 at 11:49 AM, Jiang Wu (Pricehistory) (BLOOMBERG/ 731
LEX -) <jwu...@bloomberg.net> wrote:
> Hi,
> I'm doing stress and failover tests on a 3 node 0.8.1.1 kafka cluster and
> have the following observations.
>
> A topic is created with 1 partition and 3 replications.
> request.required.acks is set to -1 for a sync producer. When the publishing
> speed is high (3M messages, each 2000 bytes, published in lists of size
> 2000), the two followers will fail out of sync. Only the leader remains in
> ISR. But the producer can keep sending. If the leader is killed with CTR_C,
> one follower will become leader, but message loss will happen because of
> the unclean leader election.
>
> In the same test, request.required.acks=3 gives the desired result.
> Followers will fail out of sync, but the producer will be blocked untill
> all followers back to ISR. No data loss is observed in this case.
>
> From the code, this turns out to be how it's designed:
> if ((requiredAcks < 0 && numAcks >= inSyncReplicas.size) ||
> (requiredAcks > 0 && numAcks >= requiredAcks)) {
> /*
> * requiredAcks < 0 means acknowledge after all replicas in ISR
> * are fully caught up to the (local) leader's offset
> * corresponding to this produce request.
> */
> (true, ErrorMapping.NoError)
> }
>
> I'm wondering if it's more reasonable to let request.required.acks=-1 mean
> "receive acks from all replicas" instead of "receive acks from replicas in
> ISR"? As in the above test, follower will fail out sync under high
> publishing volume; that makes request.required.acks=-1 equivalent to
> request.required.acks=1. Since the kafka document states
> request.required.acks=-1 provides the best durability, one would expect it
> is equivalent to request.required.acks=number_of_replications.
>
> Regards,
> Jiang
--
-- Guozhang
