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https://issues.apache.org/jira/browse/KAFKA-813?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13608130#comment-13608130
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Swapnil Ghike commented on KAFKA-813:
-------------------------------------

A couple of comments/questions before uploading the next patch:

[~junrao]: 
20. Because initializeLeaderAndIsrForPartition() is called at only one place, 
in handleStateChange(). And handleStateChange() puts the partition in Online 
state.
21. Ok, renaming to NoReplicaOnlineException.
22. Ok, also please read below.

[~nehanarkhede]: 
1.1 I agree that having all the replicas assigned to a partition down is a 
dangerous situation. I guess that will be reflected if the 
OfflinePartitionsCount is non-zero for a while, and then we can dig into Zk. An 
OfflinePartitionsCount that remains non-zero for a while could also indicate 
another dangerous situation where the replicas are up but leader is not being 
assigned. So, i think that clues provided by an OfflinePartitionsCount that 
remains non-zero for a few minutes subsume the clues given by 
UnavailablePartitionsCount, and we may not specifically need the latter. 
Thoughts?

2. Argh, yes, thanks.

3. I agree that Controller does not need to know about a useless leader 
selector. Moving NoOpLeaderSelector object to partition state machine. 

[~junrao],[~nehanarkhede]: :1.2 I believe the reason was to initialize the 
gauges when the controller object is created. However, we can move the gauges 
to ControllerStats and force their initialization like server.registerStats(). 
So perhaps it would be good if we could decide which jmx beans need to be 
force-initialized and at which places in the code. Accordingly I can make the 
relevant changes. 

                
> Minor cleanup in Controller
> ---------------------------
>
>                 Key: KAFKA-813
>                 URL: https://issues.apache.org/jira/browse/KAFKA-813
>             Project: Kafka
>          Issue Type: Bug
>    Affects Versions: 0.8
>            Reporter: Swapnil Ghike
>            Assignee: Swapnil Ghike
>            Priority: Blocker
>              Labels: kafka-0.8
>             Fix For: 0.8
>
>         Attachments: kafka-813-v1.patch, kafka-813-v2.patch
>
>
> Before starting work on delete topic support, uploading a patch first to 
> address some minor hiccups that touch a bunch of files:
> 1. Change PartitionOfflineException to PartitionUnavailableException because 
> in the partition state machine we mark a partition offline when its leader is 
> down, whereas the PartitionOfflineException is thrown when all the assigned 
> replicas of the partition are down.
> 2. Change PartitionOfflineRate to UnavailablePartitionRate
> 3. Remove default leader selector from partition state machine's 
> handleStateChange. We can specify null as default when we don't need to use a 
> leader selector.
> 4. Include controller info in the client id of LeaderAndIsrRequest.
> 5. Rename controllerContext.allleaders to something more meaningful - 
> partitionLeadershipInfo.
> 6. We don't need to put partition in OnlinePartition state in partition state 
> machine initializeLeaderAndIsrForPartition, the state change occurs in 
> handleStateChange.
> 7. Add todo in handleStateChanges
> 8. Left a comment above ReassignedPartitionLeaderSelector that reassigned 
> replicas are already in the ISR (this is not true for other leader 
> selectors), renamed the vals in the selector.

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