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From Guozhang Wang <wangg...@gmail.com>
Subject Re: Producer can writes to a follower during preferred lead election?
Date Mon, 08 Dec 2014 21:01:16 GMT
Xiaoyu,

I think your question is whether the following sequence can happen?

1. A received becomes-leader, stop fetching from B.
2. B received a producer request, and accepts it and append to log.
3. B received becomes-follower, cap its log and start fetching from A, and
hence the message sent on step 2) will be lost even the producer gets acked
from B.

Since controller sends the leaderAndIsr request to all the replicas (both
leader and followers) at the same time this is possible to happen with ack
<=1. With ack > 1 since the produce request will not be returned to the
producer until it has been replicated the above scenario will not happen.

Guozhang

On Mon, Dec 8, 2014 at 11:29 AM, Gwen Shapira <gshapira@cloudera.com> wrote:

> I think that A will not be able to become a follower until B becomes a
> leader.
>
> On Sun, Dec 7, 2014 at 11:07 AM, Xiaoyu Wang <xwang@rocketfuel.com> wrote:
> > On preferred replica election, controller sends LeaderAndIsr requests to
> > brokers. Broker will handle the LeaderAndIsr request by either become a
> > leader or become a follower.
> >
> > In the previous case, when A receive the call, it will try to become the
> > leader and stop fetching from B; when B receive the call, it will try to
> > become a follower and stop receiving new requests. Is it possible that A
> > stops fetching before B stops receiving new requests? If this is
> possible,
> > there still may be messages goes to B but not A, right?
> >
> > On Sun, Dec 7, 2014 at 7:20 AM, Thunder Stumpges <tstumpges@ntent.com>
> > wrote:
> >
> >> In this case B will return "not leader for partition" error as soon as
> the
> >> leader is re-elected and I imagine the producer will correct itself.
> >>
> >> -Thunder
> >>
> >>
> >> -----Original Message-----
> >> From: Xiaoyu Wang [xwang@rocketfuel.com]
> >> Received: Saturday, 06 Dec 2014, 6:49PM
> >> To: users@kafka.apache.org [users@kafka.apache.org]
> >> Subject: Producer can writes to a follower during preferred lead
> election?
> >>
> >> Hello,
> >>
> >> I am looking at producer code and found that producer updates its
> >> broker/partition info under the two conditions
> >>
> >>    1. has reached the topicMetadataRefreshInterval
> >>    2. failed sending message, before retry
> >>
> >> So, assume we have broker A and B, B is the current lead and A is the
> >> preferred lead and a producer is publishing to B. If someone execute
> >> preferred lead election command now, A will become the new lead and the
> >> producer won't know the lead is now A and will still writes to B until
> the
> >> metadata refresh interval has been reached. Is this correct? Or did I
> did
> >> miss anything.
> >>
> >>
> >> Thanks.
> >>
>



-- 
-- Guozhang

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