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https://issues.apache.org/jira/browse/ZOOKEEPER-2447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15355922#comment-15355922
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Edward Ribeiro commented on ZOOKEEPER-2447:
-------------------------------------------
{quote}
It will add unnecessary additional latency (the RTT latency for TCP handshake)
and overhead to every connection, even successful ones where the ensemble isn't
suffering due to a down host; it'll also put a little extra load on the
servers, not just clients.
{quote}
Hi [~dbenediktson],
Yeah... I was aware of the extra pressure on the servers and, to some degree,
the cost of opening a ephemeral TCP connection on each server of my proposed
workaround. :( OTOH, {{InetAddress#isReachable()}} (quoting javadocs) will:
{quote} (try to) use ICMP ECHO REQUESTs if the privilege can be obtained,
otherwise it will try to establish a TCP connection on port 7 {quote}
If [~vishk] don't oppose, I am more than happy to see your patch for that part.
:) In the meanwhile, I will dig {{ClientCnxnSocket}} further more following
your guidelines.
Cheers,
Ed
> Zookeeper adds good delay when one of the quorum host is not reachable
> -----------------------------------------------------------------------
>
> Key: ZOOKEEPER-2447
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2447
> Project: ZooKeeper
> Issue Type: Bug
> Affects Versions: 3.4.6, 3.5.0
> Reporter: Vishal Khandelwal
> Assignee: Vishal Khandelwal
> Fix For: 3.5.3, 3.6.0
>
> Attachments: ZOOKEEPER-2447.3.5.patch, withfix.txt, withoutFix.txt
>
>
> StaticHostProvider --> resolveAndShuffle method adds all of the address which
> are valid in the quorum to the list, shuffles them and sends back to client
> connection class. If after shuffling if first node appear to be the one which
> is not reachable, Clientcnx.SendThread.run will keep on connecting to the
> failure till a timeout and the moves to a different node. This adds up random
> delay in zookeeper connection in case a host is down. Rather we could check
> if host is reachable in StaticHostProvider and ignore isReachable is false.
> Same as we do for UnknownHostException Exception.
> This can tested using following test code by providing a valid host which is
> not reachable. for quick test comment Collections.shuffle(tmpList,
> sourceOfRandomness); in StaticHostProvider.resolveAndShuffle
> {code}
> @Test
> public void test() throws Exception {
> EventsWatcher watcher = new EventsWatcher();
> QuorumUtil qu = new QuorumUtil(1);
> qu.startAll();
>
> ZooKeeper zk =
> new ZooKeeper("<hostnamet:2181," + qu.getConnString(), 180 * 1000,
> watcher);
>
> watcher.waitForConnected(CONNECTION_TIMEOUT * 5);
> Assert.assertTrue("connection Established", watcher.isConnected());
> zk.close();
> }
> {code}
> Following fix can be added to StaticHostProvider.resolveAndShuffle
> {code}
> if(taddr.isReachable(4000 // can be some value)) {
> tmpList.add(new InetSocketAddress(taddr,
> address.getPort()));
> }
> {code}
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