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https://issues.apache.org/jira/browse/HDFS-14774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=16919011#comment-16919011
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CR Hota commented on HDFS-14774:
[~jojochuang] Thanks for reporting this.
This is ok at this point. Reason being, router has 2 layers, One the server to
external clients and client to downstream namenodes. Client to downstream
namenodes (aka RouterRpcClient) is configured to retry multiple times based on
failures from downstream namenode. It also has logic to failover and try
standby namenode if standby becomes active etc. So ya retries are present
before dns comes back as null.
And if it does come back as null then parent method does send back an
appropriate IOexception.
{code:java}
if (dn == null) {
throw new IOException("Failed to find datanode, suggest to check cluster"
+ " health. excludeDatanodes=" + excludeDatanodes);
}
{code}
Let me know if this helps ?
> RBF: Improve RouterWebhdfsMethods#chooseDatanode() error handling
> -
>
> Key: HDFS-14774
> URL: https://issues.apache.org/jira/browse/HDFS-14774
> Project: Hadoop HDFS
> Issue Type: Improvement
>Reporter: Wei-Chiu Chuang
>Assignee: CR Hota
>Priority: Minor
>
> HDFS-13972 added the following code:
> {code}
> try {
> dns = rpcServer.getDatanodeReport(DatanodeReportType.LIVE);
> } catch (IOException e) {
> LOG.error("Cannot get the datanodes from the RPC server", e);
> } finally {
> // Reset ugi to remote user for remaining operations.
> RouterRpcServer.resetCurrentUser();
> }
> HashSet excludes = new HashSet();
> if (excludeDatanodes != null) {
> Collection collection =
> getTrimmedStringCollection(excludeDatanodes);
> for (DatanodeInfo dn : dns) {
> if (collection.contains(dn.getName())) {
> excludes.add(dn);
> }
> }
> }
> {code}
> If {{rpcServer.getDatanodeReport()}} throws an exception, {{dns}} will become
> null. This does't look like the best way to handle the exception. Should
> router retry upon exception? Does it perform retry automatically under the
> hood?
> [~crh] [~brahmareddy]
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