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From "Noble Paul (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-12999) Index replication could delete segments first
Date Wed, 16 Jan 2019 03:01:00 GMT

    [ https://issues.apache.org/jira/browse/SOLR-12999?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16743575#comment-16743575
] 

Noble Paul commented on SOLR-12999:
-----------------------------------

bq. Can you please clarify what you mean by "full replication"?

A full replication is performed when there are segments in master index with same name but
different size/checksum. It used to be less common in the past with master-slave setup , but
it's now very common with leader-replica setup in SolrCloud.


bq.For example, we often found ourselves in situations where...
Well, in your case it has downloaded the entire leader index to a new directory




> Index replication could delete segments first
> ---------------------------------------------
>
>                 Key: SOLR-12999
>                 URL: https://issues.apache.org/jira/browse/SOLR-12999
>             Project: Solr
>          Issue Type: Improvement
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: replication (java)
>            Reporter: David Smiley
>            Priority: Major
>
> 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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