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From Grant Ingersoll <gsing...@apache.org>
Subject Re: Field.Store.Compress - does it improve performance of document reads?
Date Thu, 17 May 2007 11:39:56 GMT
I haven't tried compression either.  I know there was some talk a  
while ago about deprecating, but that hasn't happened.  The current  
implementation yields the highest level of compression.  You might  
find better results by compressing in your application and storing as  
a binary field, thus giving you more control over CPU used.  This is  
our current recommendation for dealing w/ compression.

If you are not actually displaying that field, you should look into  
the FieldSelector API (via IndexReader).  It allows you to lazily  
load fields or skip them all together and can yield a pretty  
significant savings when it comes to loading documents.   
FieldSelector is available in 2.1.

-Grant

On May 17, 2007, at 4:01 AM, Paul Elschot wrote:

> On Thursday 17 May 2007 08:10, Andreas Guther wrote:
>> I am currently exploring how to solve performance problems I  
>> encounter with
>> Lucene document reads.
>>
>> We have amongst other fields one field (default) storing all  
>> searchable
>> fields.  This field can become of considerable size since we are   
>> indexing
>> documents and  store the content for display within results.
>>
>> I noticed that the read can be very expensive.  I wonder now if it  
>> would
>> make sense to add this field as Field.Store.Compress to the  
>> index.  Can
>> someone tell me if this would speed up the document read or if  
>> this is
>> something only interesting for saving space.
>
> I have not tried the compression yet, but in my experience a good way
> to reduce the costs of document reads from a disk is by reading them
> in document number order whenever possible. In this way one saves
> on the disk head seeks.
> Compression should actually help reducing the costs of disk head seeks
> even more.
>
> Regards,
> Paul Elschot
>
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--------------------------
Grant Ingersoll
Center for Natural Language Processing
http://www.cnlp.org/tech/lucene.asp

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