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Date: Thu, 1 Oct 2009 08:39:49 -0700
Message-ID: <8a02878f0910010839w33e84912r77da265b4efac562@mail.gmail.com>
Subject: Re: Views
From: Jesse Hallett <hallettj@gmail.com>
To: dev@couchdb.apache.org
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Every row emitted by the map function retains a reference to the original
document.  In addition to that any data emitted by the map function is
duplicated in the view data.  This is why one common strategy is to
`emit(doc.someKey, null)`.  That way you can use the `includedocs=true`
option in queries to get document data while using as little disk space as
possible for the view.  But the downside is that this requires an additional
btree traversal for every row returned by the query to get the original
document data.

For each view the outputs from the map function and reduce function are
stored separately in separate btrees.  If you have multiple views in a
design document with map functions that are byte-for-byte identical then
CouchDB will produce one btree that they all share.  This let's you use the
same map function with different reduce functions without unnecessary
duplication of view data.

On Oct 1, 2009 8:12 AM, "Amnon Lahav" <alahav@amadesa.com> wrote:

Hi ,
I have two basic questions:
 I wasn't able to understand from the documentation if a view essentially
duplicates the data (e.g. : emit(doc.code , doc)) or just keeps a reference
to the document ?
Also it's unclear to me how the same tree is used for two views that live
inside the same design document , what exactly does that mean ?
Thanks in advance .


Amnon Lahav
J2EE Developer , Admin Team
www.amadesa.com<http://www.amadesa.com/> - Web Site Testing &
Personalization to Improve Conversion

* alahav@amadesa.com<mailto:polson@amadesa.com>
Tel: Mobile: 972.544.646499

Download a complimentary copy of Forrester Research's
"Sharpening Web Site Relevance" and read how Amadesa
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