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From Camille Fournier <cami...@apache.org>
Subject Re: SyncLimit and client notifications
Date Thu, 07 Jul 2016 17:45:05 GMT
1) Yes, I believe that roughly if the follower doesn't hear from the leader
it will go from state FOLLOWING to state LOOKING, which starts on that
server a request for leader election

2) you can have ZK set to support read-only mode, which will allow reads
from read-only clients even when disconnected from quorum, see below.

3) Yes, when the follower loses quorum for whatever reason it will
disconnect the clients, which will get a CONNECTION_LOSS error and start
looking for another server to connect to. I'm actually not sure what
happens if you have a client that is in readonlymode connected to a server
that allows readonlymode, perhaps it does not get disconnected at this time
but you'd have to look at the docs.

Read Only Mode Server

(Java system property: *readonlymode.enabled*)

*New in 3.4.0:* Setting this value to true enables Read Only Mode server
support (disabled by default). ROM allows clients sessions which requested
ROM support to connect to the server even when the server might be
partitioned from the quorum. In this mode ROM clients can still read values
from the ZK service, but will be unable to write values and see changes
from other clients. See ZOOKEEPER-784 for more details.
On Jul 5, 2016 4:50 PM, "Paul K. Harter, Jr." <paul.harter@oracle.com>
wrote:

> Apologies if this has been discussed previously, but I have a few questions
>
> on the handling of SyncLimit.
>
>
>
> 1)      does a follower keep track of SyncLimit and initiate election if it
> has
> not heard from the Leader for SyncLimit, or what triggers Leader Election?
>
> 2)      can a follower continue to serve "read" requests during Leader
> Election,
> or does Leader Election pause all client activity??
>
> 3)      does a follower give its clients an explicit notification telling
> them to find
> another server to help ensure that their sessions do not time out??
> If so, when?  SyncLimit??
>
>
>
> Thanks
>
>
>
> paul
>
>

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