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From "Uwe Schindler" <>
Subject RE: Index size variation
Date Fri, 03 Mar 2017 18:37:42 GMT
Hi Chris,

as always: "it depends". Generally I would reserve space of approximately the "original" index
size. Most indexes that are continuously updated have an overhead by 40% for deleted documents.
The remaining 60% are indeed used for merging. Please also keep in mind that if IndexReaders
are open while merging, you may see not all used disk space from the directory listing, because
some files that were merged but are still open in IndexReaders already disappeared from directory
listing (deleted during merge), but still consume disk space (delete on last close POSIX semantics).

If you also "forceMerge" your index (you should never ever do this), you may temporarily need
3 times the index size.


Uwe Schindler
Achterdiek 19, D-28357 Bremen

> -----Original Message-----
> From: Chris Bamford []
> Sent: Friday, March 3, 2017 7:24 PM
> To:
> Subject: Index size variation
> Hello
> I have observed that sometimes my index size temporarily increases by a
> large amount, presumably while it it merges segments.
> Is there some documentation on this subject? I am trying to estimate total
> disk space I'll need for a project.
> Thanks
> Chris
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