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Date: Mon, 28 Jul 2008 11:11:31 -0700 (PDT)
From: "Doug Cutting (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3822) Create a public scheduler API
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    [ https://issues.apache.org/jira/browse/HADOOP-3822?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12617495#action_12617495 ] 

Doug Cutting commented on HADOOP-3822:
--------------------------------------

> he extols the virtues of interfaces over abstract classes

What are they?  Can you summarize?  Are they significant?

> So perhaps the developer API (which is "less public") is the place where it is OK to introduce interfaces [...]

Perhaps, if there are significant advantages to interfaces.  The ability to implement multiple interfaces in a single class can save a few lines of code, but doesn't really seem significant to me when compared to the huge cost of freezing the API.

I like Steve's guidelines (above) for abstract classes.  Perhaps we should document these (and more) in the wiki or someplace, and try to validate our abstract APIs against them.  There are added potential pitfalls when using abstract classes instead of interfaces, and we should work hard to avoid them.

> Create a public scheduler API
> -----------------------------
>
>                 Key: HADOOP-3822
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3822
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Tom White
>             Fix For: 0.19.0
>
>         Attachments: hadoop-3822.patch, hadoop-3822.sh
>
>
> The work in HADOOP-3412 provided an API to support pluggable schedulers. However implementations have to be in the org.apache.hadoop.mapred package, which is undesirable. The goal of this issue is to create a public API for scheduler writers to code against.

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