[jira] [Commented] (HADOOP-8304) DNSToSwitchMapping should add interface to resolve individual host besides a list of host

["Junping Du (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-8304?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13268933#comment-13268933 ] 

Junping Du commented on HADOOP-8304:
------------------------------------

That's good comments on compatibility of this change. I saw evolving tag there but not consider people extends DNSToSwitchMapping as well (just thought ScriptBased, TableMapping and cached are good enough).
I won't say original interface cause some performance headache as the time of resolving rack info can be overwhelmed comparing with the whole flow (replica placement or task scheduling). However, it is more easy to use for major consumers of original interface which are expecting to resolve individual host. Do you see any scenario to resolve a list of host? (not counting the unit test)
Eli, I don't understand the question of last comment there as I just want to fix the interface here. :)

                
> DNSToSwitchMapping should add interface to resolve individual host besides a list of host
> -----------------------------------------------------------------------------------------
>
>                 Key: HADOOP-8304
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8304
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 1.0.0, 2.0.0
>            Reporter: Junping Du
>            Assignee: Junping Du
>             Fix For: 2.0.0
>
>         Attachments: HADOOP-8304-V2.patch, HADOOP-8304-V2.patch, HADOOP-8304.patch
>
>   Original Estimate: 48h
>  Remaining Estimate: 48h
>
> DNSToSwitchMapping now has only one API to resolve a host list: public List<String> resolve(List<String> names). But the two major caller: RackResolver.resolve() and DatanodeManager.resolveNetworkLocation() are taking single host name but have to wrapper it to an single entry ArrayList. This is not necessary especially the host has been cached before.

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