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https://issues.apache.org/jira/browse/LUCENE-8310?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Simon Willnauer updated LUCENE-8310:
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    Attachment: LUCENE-8310.patch

> Relax IWs check on pending deletes
> ----------------------------------
>
>                 Key: LUCENE-8310
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8310
>             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-8310.patch
>
>
> I recently fixed the check in IW to fail if there are pending deletes. After 
> upgrading to a snapshot I realized the consequences of this check. It made 
> most of our usage of IW to for instance prepare commit metadata, rollback to 
> safe commit-points etc. impossible since we have to now busy wait on top of 
> directory util all deletes are actually gone even though that we can 
> guarantee that our history always goes forward. ie we are truly append-only 
> in the sense of never reusing segment generations. The fix that I made was 
> basically return false from a _checkPendingDeletions_ in a directory wrapper 
> to work around it.
> I do expect this to happen to a lot of lucene users even if they use IW 
> correctly. My proposal is to make the check in IW a bit more sophisticated 
> and only fail if there are pending deletes that are in the future from a 
> generation perspective. We really don't care about files from the past. My 
> patch checks the segment generation of each pending file which is safe since 
> that is the same procedure we apply in IndexFileDeleter to inc reference etc. 
> and only fail if the pending delete is in the future.



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