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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7049) add dynamic configuration update mechanism
Date Thu, 25 Oct 2012 00:08:12 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13483749#comment-13483749
] 

Sergey Shelukhin commented on HBASE-7049:
-----------------------------------------

There's also a design option here.
The current approach is the patch is an explicit admin command that is propagated to all the
requisite objects and causes them to re-read the configuration they are interested in from
disk.
I personally prefer the approach where the act of replacing the file (or adding an override
file) would cause the service configuration to be automatically updated inside the configuration
object itself.
One never caches values from config during init; config object does that on init/first request
for a value (and on config file change); thus, the code instead calls conf.getLong("MyCoolValue")
every time (or for one method call/one compaction/one request/...), and gets the recent value.
For special cases, it's easy to add mechanism to get several values atomically, and for the
most special case to add the change callback.
This avoids adding the code to propagate config to places/handling updates in code, and avoids
the non-atomicity of copying the files and then updating config via admin command.

I wonder if there are opinions for either approach?
                
> add dynamic configuration update mechanism
> ------------------------------------------
>
>                 Key: HBASE-7049
>                 URL: https://issues.apache.org/jira/browse/HBASE-7049
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.96.0
>            Reporter: Sergey Shelukhin
>            Assignee: Sergey Shelukhin
>
> Initial draft will be modeled on 0.89-fb changes; see HBASE-6371

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