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https://issues.apache.org/jira/browse/SOLR-15052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17250286#comment-17250286
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Jan Høydahl commented on SOLR-15052:
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I think this is the first place in our ZK tree that we will be allowing a
"file" znode to also have children. While fully supported in ZK, it won't
translate well to a filesystem layout. Have you considered placing the children
in a new {{replica_states}} znode instead of using the {{state.json}} znode? I
cannot say exactly what usecase would be difficult with the proposed layout,
but I have a sneaking feeling that it would be more "compatible" to limit
ourselves to either "directory" or "file" for each znode, unless the combined
approach has obvious benefits.
> Reducing overseer bottlenecks using per-replica states
> ------------------------------------------------------
>
> Key: SOLR-15052
> URL: https://issues.apache.org/jira/browse/SOLR-15052
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Ishan Chattopadhyaya
> Priority: Major
> Attachments: per-replica-states-gcp.pdf
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> This work has the same goal as SOLR-13951, that is to reduce overseer
> bottlenecks by avoiding replica state updates from going to the state.json
> via the overseer. However, the approach taken here is different from
> SOLR-13951 and hence this work supercedes that work.
> The design proposed is here:
> https://docs.google.com/document/d/1xdxpzUNmTZbk0vTMZqfen9R3ArdHokLITdiISBxCFUg/edit
> Briefly,
> # Every replica's state will be in a separate znode nested under the
> state.json. It has the name that encodes the replica name, state, leadership
> status.
> # An additional children watcher to be set on state.json for state changes.
> # Upon a state change, a ZK multi-op to delete the previous znode and add a
> new znode with new state.
> Differences between this and SOLR-13951,
> # In SOLR-13951, we planned to leverage shard terms for per shard states.
> # As a consequence, the code changes required for SOLR-13951 were massive (we
> needed a shard state provider abstraction and introduce it everywhere in the
> codebase).
> # This approach is a drastically simpler change and design.
> Credits for this design and the PR is due to [~noble.paul].
> [[email protected]], [~noble.paul] and I have collaborated on this
> effort. The reference branch takes a conceptually similar (but not identical)
> approach.
> I shall attach a PR and performance benchmarks shortly.
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