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From "Uwe Schindler" <...@thetaphi.de>
Subject RE: Stored fields and OS file caching
Date Fri, 04 Apr 2014 22:00:48 GMT
Hi,

What are you doing with the stored fields? They are not deprecated and also not really slow,
unless you scan over millions of documents in random access order. To display serach results,
DocValues are of no use.

Uwe

-----
Uwe Schindler
H.-H.-Meier-Allee 63, D-28213 Bremen
http://www.thetaphi.de
eMail: uwe@thetaphi.de


> -----Original Message-----
> From: Vitaly Funstein [mailto:vfunstein@gmail.com]
> Sent: Friday, April 04, 2014 9:44 PM
> To: java-user@lucene.apache.org
> Subject: Stored fields and OS file caching
> 
> I have heard here that stored fields don't work well with OS file caching.
> Could someone elaborate on why that is? I am using Lucene 4.6 and we do
> use stored fields but not doc values; it appears most of the benefit from the
> latter comes as improvement in sorting performance, and I don't actually use
> Lucene for sorting at all; rather, it's done on a post-processing basis, based on
> stored field values (in a nutshell, the reason for this is Lucene's inability to tell
> apart terms that are empty strings vs. a missing value, resulting in unstable
> sort order on such fields).
> 
> I am not sure if switching to using doc values fields from stored fields entirely
> would help leverage OS file cache better... what worries me is that when
> processing queries requesting multiple values from the document, doc value
> fields could cause multiple disk seeks to fetch values for each field, as
> opposed to just one with stored fields.
> 
> Am I way off in my understanding of how this works? Any guidelines, as
> general as they may be, are appreciated.


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