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https://issues.apache.org/jira/browse/SOLR-9835?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15816918#comment-15816918
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Cao Manh Dat commented on SOLR-9835:
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Thanks a lot for your comments!
bq. Maybe add a method to DocCollection like {{isOnlyLeaderIndexes()}}
As you know, we won't use {{isOnlyLeaderIndexes()}} in the future ( it won't
have enough information ), so I just do not want to add a public method on
DocCollection ( solrj ) and remove it in the future.
bq. Does this need to be synchronized?
Yeah, I think we should.
bq. should masterUrl now be volatile?
I don't see any reason why we need masterUrl to be volatile? IndexFetcher
instance is not being shared across threads.
bq. In many cases in the tests the leader will change before the replication
happens, right? Does it make sense to discover the leader inside of the loop?
Also, is there a way to remove that Thread.sleep(1000) at the beginning? This
code will be called very frequently in tests.
That's a good idea.
> Create another replication mode for SolrCloud
> ---------------------------------------------
>
> Key: SOLR-9835
> URL: https://issues.apache.org/jira/browse/SOLR-9835
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Cao Manh Dat
> Assignee: Shalin Shekhar Mangar
> Attachments: SOLR-9835.patch, SOLR-9835.patch, SOLR-9835.patch,
> SOLR-9835.patch, SOLR-9835.patch, SOLR-9835.patch
>
>
> The current replication mechanism of SolrCloud is called state machine, which
> replicas start in same initial state and for each input, the input is
> distributed across replicas so all replicas will end up with same next state.
> But this type of replication have some drawbacks
> - The commit (which costly) have to run on all replicas
> - Slow recovery, because if replica miss more than N updates on its down
> time, the replica have to download entire index from its leader.
> So we create create another replication mode for SolrCloud called state
> transfer, which acts like master/slave replication. In basically
> - Leader distribute the update to other replicas, but the leader only apply
> the update to IW, other replicas just store the update to UpdateLog (act like
> replication).
> - Replicas frequently polling the latest segments from leader.
> Pros:
> - Lightweight for indexing, because only leader are running the commit,
> updates.
> - Very fast recovery, replicas just have to download the missing segments.
> To use this new replication mode, a new collection must be created with an
> additional parameter {{liveReplicas=1}}
> {code}
> http://localhost:8983/solr/admin/collections?action=CREATE&name=newCollection&numShards=2&replicationFactor=1&liveReplicas=1
> {code}
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