[
https://issues.apache.org/jira/browse/KAFKA-1555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14191202#comment-14191202
]
Gwen Shapira commented on KAFKA-1555:
-------------------------------------
" it is independent of the producer's ack config"
Actually, it is not. min.insync.replicas has no effect unless acks=-1. I hope
the documentation makes that clear.
min.insync.replicas is used within delayedProduce() to decide when enough
replicas acked the message. Is that what you mean by "declare committed"? Part
of the change (and maybe an unfortunate part) was to push awareness of
request.required.acks to this part of the code, so we'll know when to throw
NotEnoughReplicasException.
I'm ok swapping the order and starting by explaining about ISR size and
guarantees, but I'm pretty sure the connection with request.required.acks is
important to point out. The feature doesn't fully makes sense without it (at
least it doesn't when I explain it...)
> provide strong consistency with reasonable availability
> -------------------------------------------------------
>
> Key: KAFKA-1555
> URL: https://issues.apache.org/jira/browse/KAFKA-1555
> Project: Kafka
> Issue Type: Improvement
> Components: controller
> Affects Versions: 0.8.1.1
> Reporter: Jiang Wu
> Assignee: Gwen Shapira
> Fix For: 0.8.2
>
> Attachments: KAFKA-1555-DOCS.0.patch, KAFKA-1555-DOCS.1.patch,
> KAFKA-1555-DOCS.2.patch, KAFKA-1555.0.patch, KAFKA-1555.1.patch,
> KAFKA-1555.2.patch, KAFKA-1555.3.patch, KAFKA-1555.4.patch,
> KAFKA-1555.5.patch, KAFKA-1555.5.patch, KAFKA-1555.6.patch,
> KAFKA-1555.8.patch, KAFKA-1555.9.patch
>
>
> In a mission critical application, we expect a kafka cluster with 3 brokers
> can satisfy two requirements:
> 1. When 1 broker is down, no message loss or service blocking happens.
> 2. In worse cases such as two brokers are down, service can be blocked, but
> no message loss happens.
> We found that current kafka versoin (0.8.1.1) cannot achieve the requirements
> due to its three behaviors:
> 1. when choosing a new leader from 2 followers in ISR, the one with less
> messages may be chosen as the leader.
> 2. even when replica.lag.max.messages=0, a follower can stay in ISR when it
> has less messages than the leader.
> 3. ISR can contains only 1 broker, therefore acknowledged messages may be
> stored in only 1 broker.
> The following is an analytical proof.
> We consider a cluster with 3 brokers and a topic with 3 replicas, and assume
> that at the beginning, all 3 replicas, leader A, followers B and C, are in
> sync, i.e., they have the same messages and are all in ISR.
> According to the value of request.required.acks (acks for short), there are
> the following cases.
> 1. acks=0, 1, 3. Obviously these settings do not satisfy the requirement.
> 2. acks=2. Producer sends a message m. It's acknowledged by A and B. At this
> time, although C hasn't received m, C is still in ISR. If A is killed, C can
> be elected as the new leader, and consumers will miss m.
> 3. acks=-1. B and C restart and are removed from ISR. Producer sends a
> message m to A, and receives an acknowledgement. Disk failure happens in A
> before B and C replicate m. Message m is lost.
> In summary, any existing configuration cannot satisfy the requirements.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
