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From "Simon Willnauer (JIRA)" <>
Subject [jira] [Commented] (LUCENE-8264) Allow an option to rewrite all segments
Date Mon, 14 May 2018 12:47:00 GMT


Simon Willnauer commented on LUCENE-8264:


 # For N-1 -> N we have _org.apache.lucene.index.UpgradeIndexMergePolicy_ ?
 # In order to add DV I think this should be done by wrapping a codec reader. I personally
think quite an edge case and should be done in the higher level application ie. Solr itself.
You can do this quite easily with _org.apache.lucene.index.OneMergeWrappingMergePolicy_ similar
to what we do in the soft delete case in _SoftDeletesRetentionMergePolicy_

do I miss something?


> Allow an option to rewrite all segments
> ---------------------------------------
>                 Key: LUCENE-8264
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Erick Erickson
>            Assignee: Erick Erickson
>            Priority: Major
> For the background, see SOLR-12259.
> There are several use-cases that would be much easier, especially during upgrades, if
we could specify that all segments get rewritten. 
> One example: Upgrading 5x->6x->7x. When segments are merged, they're rewritten
into the current format. However, there's no guarantee that a particular segment _ever_ gets
merged so the 6x-7x upgrade won't necessarily be successful.
> How many merge policies support this is an open question. I propose to start with TMP
and raise other JIRAs as necessary for other merge policies.
> So far the usual response has been "re-index from scratch", but that's increasingly difficult
as systems get larger.

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