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https://issues.apache.org/jira/browse/SOLR-12999?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18058939#comment-18058939
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David Smiley commented on SOLR-12999:
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I think it'd be a shame to not retain the optimization. I disagree with "data
loss" -- it's up to the leader election / "shard terms" to deem who is leader
eligible. A replica that is about to pull the whole index from another node
isn't leader eligible (right?). The implementation could take a step to
guarantee it's not marked as such (shard terms manipulation). But it's even
more of a shame that the implementation is buggy/unreliable/untested. So I
very much sympathize with removing it on that grounds. I leave it to you.
> Index replication could delete segments first
> ---------------------------------------------
>
> Key: SOLR-12999
> URL: https://issues.apache.org/jira/browse/SOLR-12999
> Project: Solr
> Issue Type: Improvement
> Components: replication (java)
> Reporter: David Smiley
> Assignee: Noble Paul
> Priority: Major
> Fix For: 8.1
>
> Attachments: SOLR-12999.patch, SOLR-12999.patch
>
>
> Index replication could optionally delete files that it knows will not be
> needed _first_. This would reduce disk capacity requirements of Solr, and it
> would reduce some disk fragmentation when space get tight.
> Solr (IndexFetcher) already grabs the remote file list, and it could see
> which files it has locally, then delete the others. Today it asks Lucene to
> {{deleteUnusedFiles}} at the end. This new mode would probably only be
> useful if there is no SolrIndexSearcher open, since it would prevent the
> removal of files.
> The motivating scenario is a SolrCloud replica that is going into full
> recovery. It ought to not be fielding searches. The code changes would not
> depend on SolrCloud though.
> This option would have some danger the user should be aware of. If the
> replication fails, leaving the local files incomplete/corrupt, the only
> recourse is to try full replication again. You can't just give up and field
> queries.
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