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From SuoNayi <suonayi2...@163.com>
Subject Re:Re: 3 general questions about SolrCloud
Date Tue, 16 Apr 2013 05:24:32 GMT
Thanks for clarification and I think I did make it clear.



At 2013-04-16 01:59:59,"Shawn Heisey" <solr@elyograg.org> wrote:
>On 4/15/2013 9:58 AM, SuoNayi wrote:
>> 1. What's the model between the master and replicas in one shard?
>> If the replicas are able to catch up with the master when the master
>> receives a update request it will scatter the request to all the active
>> replicas and expect responses before the request get executed
>> by itself.This is called push model,right?
>> When a new replica is present it will download the whole index from
>> the master can this be called pull model?but when the master pushes
>> updates to it how the replica behaves,continuing to download the whole
>> index while keeping a track of the updates in a log(tlog) ?
>
>There is no master.  SolrCloud is fully distributed.  One replica on 
>each shard is elected leader, but that is not a permanent designation.
>
>> 2.What's the main use of the transaction log?
>> Is it only used to serve the NRT get requests and not related with data sync
>> between the master and replica?
>
>The transaction log is used to replay transactions when a node starts 
>up.  If the differences between the leader replica and a replica that 
>just started are small enough, the transaction log will be used to bring 
>them back into sync.  If they are too different, the one that just 
>started will replicate the full index from the leader.  I am pretty sure 
>that the _version_ field present on every document is used to determine 
>whether replicas are in sync, not the index version.
>
>> 3.Will the leader election be related with index version?
>> If a shard has 3 replicas and when the master goes down how to choose the master,
>> do they compare the lastest index version for each one or only consider the earliest
presence time?
>
>Here is my understanding about leader elections, I hope it's right! 
>Leader elections only take place when the leader goes down.  Once a 
>replica is elected leader, it will remain leader unless it goes down. 
>The other replicas can go up and down and the leader will retain that 
>role.  I do not think the index version is used at all, the _version_ 
>field in the index is probably used instead.
>
>Thanks,
>Shawn
>

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