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https://issues.apache.org/jira/browse/SOLR-12509?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrzej Bialecki resolved SOLR-12509.
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Resolution: Fixed
> Improve SplitShardCmd performance and reliability
> -------------------------------------------------
>
> Key: SOLR-12509
> URL: https://issues.apache.org/jira/browse/SOLR-12509
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Reporter: Andrzej Bialecki
> Assignee: Andrzej Bialecki
> Priority: Major
> Fix For: 7.5
>
> Attachments: SOLR-12509.patch, SOLR-12509.patch
>
>
> {{SplitShardCmd}} is currently quite complex.
> Shard splitting occurs on active shards, which are still being updated, so
> the splitting has to involve several carefully orchestrated steps, making
> sure that new sub-shard placeholders are properly created and visible, and
> then also applying buffered updates to the split leaders and performing
> recovery on sub-shard replicas.
> This process could be simplified in cases where collections are not actively
> being updated or can tolerate a little downtime - we could put the shard
> "offline", ie. disable writing while the splitting is in progress (in order
> to avoid users' confusion we should disable writing to the whole collection).
> The actual index splitting could perhaps be improved to use
> {{HardLinkCopyDirectoryWrapper}} for creating a copy of the index by
> hard-linking existing index segments, and then applying deletes to the
> documents that don't belong in a sub-shard. However, the resulting index
> slices that replicas would have to pull would be the same size as the whole
> shard.
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