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https://issues.apache.org/jira/browse/HDFS-16831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17651034#comment-17651034
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ASF GitHub Bot commented on HDFS-16831:
---------------------------------------
ZanderXu commented on PR #5098:
URL: https://github.com/apache/hadoop/pull/5098#issuecomment-1362283212
\
> To test the shuffling, one approach would be to call
namenodeResolver.getNamenodesForNameserviceId() 100 times in a loop and check
if ever the two observers swap positions in the list. If there is never a swap
we fail the test.
>
> The test will be probabilistic but the chance of it flaking will be
extremely low 0.5^100.
>
> ```
> List<? extends FederationNamenodeContext> observerList3 ;
> for(int i = 0; i < 100; i++) {
> observerList3 =
namenodeResolver.getNamenodesForNameserviceId(NAMESERVICES[0], true);
> assertEquals(FederationNamenodeServiceState.OBSERVER,
observerList3.get(0).getState());
> assertEquals(FederationNamenodeServiceState.OBSERVER,
observerList3.get(1).getState());
> if
(observerList3.get(0).getNamenodeId().equals(observerList2.get(1).getNamenodeId())
&&
>
observerList3.get(1).getNamenodeId().equals(observerList2.get(0).getNamenodeId()))
{
> return;
> }
> }
> Assert.fail("Observer order never changed.");
> ```
@simbadzina Thanks for your nice suggestion, I will do it.
> [RBF SBN] GetNamenodesForNameserviceId should shuffle Observer NameNodes
> every time
> -----------------------------------------------------------------------------------
>
> Key: HDFS-16831
> URL: https://issues.apache.org/jira/browse/HDFS-16831
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: ZanderXu
> Assignee: ZanderXu
> Priority: Major
> Labels: pull-request-available
>
> The method getNamenodesForNameserviceId in MembershipNamenodeResolver.class
> should shuffle Observer NameNodes every time. The current logic will return
> the cached list and will caused all of read requests are forwarding to the
> first observer namenode.
>
> The related code as bellow:
> {code:java}
> @Override
> public List<? extends FederationNamenodeContext> getNamenodesForNameserviceId(
> final String nsId, boolean listObserversFirst) throws IOException {
> List<? extends FederationNamenodeContext> ret = cacheNS.get(Pair.of(nsId,
> listObserversFirst));
> if (ret != null) {
> return ret;
> }
> ...
> }{code}
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