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https://issues.apache.org/jira/browse/ZOOKEEPER-2466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15368703#comment-15368703
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Michael Han commented on ZOOKEEPER-2466:
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I am thinking we can do this:
# Remove addrvec_next in handle_error. Make it clear that handle_error only
does clean up / logging work. If we need to try another server, we need
explicitly call zoo_cycle_server or addrvec_next.
# For read only state processing, I am thinking we could do this (after
addrvec_next is removed from handle_error), because if we are here then the
current server is not usable anyway (either it is a dead server or a read-write
server, and we need a read only server if I understand this logic correctly),
so we'd move on and try another server.
{code}
if (ping_rw_server(zh)) {
struct sockaddr_storage addr;
addrvec_peek(&zh->addrs, &addr);
zh->ping_rw_timeout = MIN_RW_TIMEOUT;
LOG_INFO(LOGCALLBACK(zh),
"r/w server found at %s",
format_endpoint_info(&addr));
handle_error(zh, ZRWSERVERFOUND);
}
addrvec_next(&zh->addrs, NULL);
{code}
> 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: Flavio Junqueira
> Priority: Critical
> Fix For: 3.5.3, 3.6.0
>
>
> 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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