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https://issues.apache.org/jira/browse/ZOOKEEPER-2466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15383563#comment-15383563
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Flavio Junqueira commented on ZOOKEEPER-2466:
---------------------------------------------
[~hanm] as you explained, there is a behavior change since with RO status the
client won't look for an RW server until the reconfig completes. Say that it
disconnects from the RO server, though, maybe because the RO server has been
removed from the configuration. What happens in this case? I'd expect that
either it looks for another RO server or it waits until the reconfig completes,
although the former is more aligned with the behavior we describe in the
documentation.
Also, I was thinking if we need a test case for this. We found out about this
problem through a test case, but apparently it doesn't always fails. It might
be worth checking that the order of servers is as expected.
> Client skips servers when trying to connect
> -------------------------------------------
>
> Key: ZOOKEEPER-2466
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2466
> Project: ZooKeeper
> Issue Type: Bug
> Components: c client
> Reporter: Flavio Junqueira
> Assignee: Michael Han
> Priority: Critical
> Fix For: 3.5.3, 3.6.0
>
> Attachments: ZOOKEEPER-2466.patch
>
>
> I've been looking at {{Zookeeper_simpleSystem::testFirstServerDown}} and I
> observed the following behavior. The list of servers to connect contains two
> servers, let's call them S1 and S2. The client never connects, but the odd
> bit is the sequence of servers that the client tries to connect to:
> {noformat}
> S1
> S2
> S1
> S1
> S1
> <keeps repeating S1>
> {noformat}
> It intrigued me that S2 is only tried once and never again. Checking the
> code, here is what happens. Initially, {{zh->reconfig}} is 1, so in
> {{zoo_cycle_next_server}} we return an address from
> {{get_next_server_in_reconfig}}, which is taken from {{zh->addrs_new}} in
> this test case. The attempt to connect fails, and {{handle_error}} is invoked
> in the error handling path. {{handle_error}} actually invokes
> {{addrvec_next}} which changes the address pointer to the next server on the
> list.
> After two attempts, it decides that it has tried all servers in
> {{zoo_cycle_next_server}} and sets {{zh->reconfig}} to zero. Once
> {{zh->reconfig == 0}}, we have that each call to {{zoo_cycle_next_server}}
> moves the address pointer to the next server in {{zh->addrs}}. But, given
> that {{handle_error}} also moves the pointer to the next server, we end up
> moving the pointer ahead twice upon every failed attempt to connect, which is
> wrong.
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