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https://issues.apache.org/jira/browse/LUCENE-8233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16423361#comment-16423361
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Robert Muir commented on LUCENE-8233:
-------------------------------------

I think the overall idea is interesting. So the user's "api" is to just 
indicate a field name to indexwriter to be used for soft deletes, similar to 
using an active=Y/N field for a relational database or whatever. I think thats 
intuitive.

The main thing confusing me is the exact docs around that:

{quote}
Returns the field that should be used to find soft deletes. If soft deletes are 
used all documents that have a doc values value in this field are treated as 
deleted. The default is null.
{quote}

Can we expand the doc on this to explain it a bit more for a typical use-case? 
e.g.:
* how to soft-delete a doc (fairly obvious)
* how to undelete (this part is not obvious to me at the moment)
* how to configure a reasonable merge policy, say with a 7-day retention of 
soft deletes or some other reasonable example (there is a test for this case, 
but its trying to really exercise the merge policy and difficult as an example)



>  Add support for soft deletes to IndexWriter delete accounting
> --------------------------------------------------------------
>
>                 Key: LUCENE-8233
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8233
>             Project: Lucene - Core
>          Issue Type: Improvement
>    Affects Versions: 7.4, master (8.0)
>            Reporter: Simon Willnauer
>            Priority: Major
>             Fix For: 7.4, master (8.0)
>
>         Attachments: LUCENE-8233.patch, LUCENE-8233.patch
>
>
> This change adds support for soft deletes as a fully supported feature by the 
> index writer. Soft deletes are accounted for inside the index writer and 
> therefor also by merge policies.
>     
> This change also adds a SoftDeletesRetentionMergePolicy that allows users to 
> selectively carry over soft_deleted document across merges for retention 
> policies. The merge policy selects documents that should be kept around in 
> the merged segment based on a user provided query.



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