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https://issues.apache.org/jira/browse/LUCENE-5941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14131561#comment-14131561
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Shai Erera edited comment on LUCENE-5941 at 9/12/14 2:04 PM:
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I added {{dir.setEnableVirusScanner(false);}}, but the test still fails (and I 
verify that before the failure virus scanner is indeed disabled.. I will 
disable virus scanner for this test anyway though, because it asserts disk 
usage and we don't want any surprises.


was (Author: shaie):
I added {{dir.setEnableVirusScanner(false);}}, but the test still fails (and I 
verify that before the failure virus scanner is indeed disabled..

> IndexWriter.forceMerge documentation error
> ------------------------------------------
>
>                 Key: LUCENE-5941
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5941
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/index
>            Reporter: Shai Erera
>            Assignee: Shai Erera
>         Attachments: LUCENE-5941.patch
>
>
> IndexWriter.forceMerge documents that it requires up to 3X *FREE* space in 
> order to run successfully. We even go further with it and test it in 
> TestIWForceMerge.testForceMergeTempSpaceUsage(). But I think that's wrong. I 
> cannot think of a situation where we consume 3X *additional* space during 
> merge:
> * 1X - that's the source segments to be merged
> * 2X - that's the result non-CFS merged segment
> * 3X - that's the CFS creation
> At no point do we publish the non-CFS merged segment, therefore the merge, as 
> I understand it, only consumes up to 2X additional space during that merge.
> And anyway, we only require 2X of additional space of the *largest* merge (or 
> total batch of running merges, depends on your MergeScheduler), not the whole 
> index size. This is an important observation, since if you e.g. have a 500GB 
> index, users shouldn't think they need to reserve an additional 1TB for 
> merging, since most of their big segments won't be merged by default anyway 
> (TieredMP defaults to 5GB largest segment).
> I'll post a patch which fixes the documentation and the test. If anyone can 
> think of a scenario where we consume up to 3X *additional* space, please 
> chime, and I'll only modify IW.forceMerge documentation to explain that.



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