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https://issues.apache.org/jira/browse/HDFS-13845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16597018#comment-16597018
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yanghuafeng commented on HDFS-13845:
------------------------------------
improve some unit tests.
{quote}
The only part that is a little confusing ins getClass() ==
MountTableResolver.class.
What happens when we invoke this from one of the ordered resolvers?
{quote}
getClass() will return the real class of the instance. For example, when you
invoke this method buildLocation from the MultipleDestinationMountableResolver,
it does not equal the MountableResolver.class because you have got the
MultipleDestinationMountableResolver.class
> RBF: The default MountTableResolver should fail resolving multi-destination
> paths
> ---------------------------------------------------------------------------------
>
> Key: HDFS-13845
> URL: https://issues.apache.org/jira/browse/HDFS-13845
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: federation, hdfs
> Affects Versions: 3.0.0, 3.1.0, 2.9.1
> Reporter: yanghuafeng
> Assignee: yanghuafeng
> Priority: Major
> Attachments: HDFS-13845.001.patch, HDFS-13845.002.patch
>
>
> When we use the default MountTableResolver to resolve the path, we cannot get
> the destination paths for the default DestinationOrder.HASH.
> {code:java}
> // Some comments here
> private static PathLocation buildLocation(
> ......
> List<RemoteLocation> locations = new LinkedList<>();
> for (RemoteLocation oneDst : entry.getDestinations()) {
> String nsId = oneDst.getNameserviceId();
> String dest = oneDst.getDest();
> String newPath = dest;
> if (!newPath.endsWith(Path.SEPARATOR) && !remainingPath.isEmpty()) {
> newPath += Path.SEPARATOR;
> }
> newPath += remainingPath;
> RemoteLocation remoteLocation = new RemoteLocation(nsId, newPath, path);
> locations.add(remoteLocation);
> }
> DestinationOrder order = entry.getDestOrder();
> return new PathLocation(srcPath, locations, order);
> }
> {code}
> The default order will be hash, but the HashFirstResolver will not be invoked
> to order the location.
> It is ambiguous for the MountTableResolver that we will see the HASH order in
> the web ui for multi-destinations path but we cannot get the result.
> In my opinion, the MountTableResolver will be a simple resolver to implement
> 1 to 1 not including the 1 to n destinations. So we should check the
> buildLocation. If the entry has multi destinations, we should reject it.
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