[jira] Commented: (HADOOP-6078) Ability to re-configure hadoop daemons online

["Todd Lipcon (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-6078?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12721421#action_12721421 ] 

Todd Lipcon commented on HADOOP-6078:
-------------------------------------

I like this idea. Here are a couple thoughts:
- In addition to having a whitelist of reloadable properties, we should generate loud warnings about any config properties that are modified but are *not* whitelisted. Something like:

ERROR: configuration property fs.default.name modified on disk but not is not reloadable. Retaining old value.

These errors would ideally spit out on the console of the operator, not just in the log4j output on the server side.

- We should also probably have diagnostic output for any changes that did take effect. For example:

INFO: Configuration property foo.bar changed from "blah" to "blahblah"

- Does this introduce the need for additional synchronization inside Configuration?

> Ability to re-configure hadoop daemons online
> ---------------------------------------------
>
>                 Key: HADOOP-6078
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6078
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>            Reporter: Amar Kamat
>
> Example : 
> Like we have _bin hadoop mradmin -refreshNodes_ we should also have _bin hadoop mradmin -reconfigure_ which re-configures mr while the cluster is online. Few parameters like job-expiry-interval etc can be changed in this way without having to restart the whole cluster. 
> Master, once reconfigured, can ask the slaves to reconfigure (reload its config) from a well defined location on hdfs or via heartbeat. 
> We can have some whitelisted configs that have _reloadable_ property. 

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