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https://issues.apache.org/jira/browse/SOLR-14306?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17052383#comment-17052383
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Tomas Eduardo Fernandez Lobbe commented on SOLR-14306:
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Thanks Jan. I think with the right interfaces, we should be able to replace the
underlying implementation we use for coordination (either one of those you
suggested or maybe others we haven't thought of). While make them pluggable is
out of the scope of this particular SIP, I think it's a step on that direction.
If we decide to not make it pluggable, and never to change ZooKeeper, this is
still important to improve testing IMO.
> Refactor coordination code into separate module and evaluate using Curator
> --------------------------------------------------------------------------
>
> Key: SOLR-14306
> URL: https://issues.apache.org/jira/browse/SOLR-14306
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Reporter: Tomas Eduardo Fernandez Lobbe
> Priority: Major
>
> This Jira issue is to discuss two changes that unfortunately are difficult to
> address separately
> # Separate all ZooKeeper coordination logic into it’s own module, that can
> be tested in isolation
> # Evaluate using Apache Curator for coordination instead of our own logic.
> I drafted a
> [SIP|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=148640472],
> but this is very much WIP, I’d like to hear opinions before I spend too much
> time on something people hates.
> From the initial draft of the SIP:
> {quote}The main goal of this change is to allow better testing of the
> different ZooKeeper interactions related to coordination (leader election,
> queues, etc).
There are already some abstractions in place for lower level
> operations (set-data, get-data, etc, see DistribStateManager), so the idea is
> to have a new, related abstraction named CoordinationManager, where we could
> have some higher level coordination-related classes, like LeaderRunner
> (Overseer), LeaderLatch (for shard leaders), etc.
Curator comes into place
> because, in order to refactor the existing code into these new abstractions,
> we’d have to rework much of it, so we could instead consider using Curator, a
> library that was mentioned in the past many times. While I don’t think this
> is required, It would make this transition and our code simpler (from what I
> could see, however, input from people with more Curator experience would be
> greatly appreciated).
> While it would be out of the scope of this change, If the
> abstractions/interfaces are correctly designed, this could lead to, in the
> future, be able to use something other than ZooKeeper for coordination,
> either etcd or maybe even some in-memory replacement for tests.
> {quote}
> There are still many open questions, and many questions I still don’t know
> we’ll have, but please, let me know if you have any early feedback, specially
> if you’ve worked with Curator in the past.
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