Mailing-List: contact user-help@couchdb.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@couchdb.apache.org
Received-SPF: pass (nike.apache.org: domain of djc.ochtman@gmail.com
 designates 209.85.216.173 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:sender:in-reply-to:references:from:date
         :x-google-sender-auth:message-id:subject:to:content-type;
        b=SaXNnxCgVF4Fw5yp233HeG7ZvQdaCCfqkQiWuK4Y4n0WDqEJ3dUPbFwQk6CifPxvDL
         NVOQTh7lY0uFYIpJ1oI1OP7zT21kCIpYgqcUsHbKDOcwdBxyPu+XrGjWOEjcHDIPqJA3
         BHvPZDeMqoORj4BwbHSF8pZQJ/8NPFa1zGV2A=
MIME-Version: 1.0
Sender: djc.ochtman@gmail.com
In-Reply-To: <BANLkTikpYTzon8YKP20_zYoGf8dzAzTNKg@mail.gmail.com>
References: <BANLkTikpYTzon8YKP20_zYoGf8dzAzTNKg@mail.gmail.com>
From: Dirkjan Ochtman <dirkjan@ochtman.nl>
Date: Sun, 19 Jun 2011 16:07:20 +0200
Message-ID: <BANLkTikve=Tsut=wgcxjnADkfwCPCp2idQ@mail.gmail.com>
Subject: Re: Is reduce not incremental?
To: user@couchdb.apache.org
Content-Type: text/plain; charset=UTF-8

On Sun, Jun 19, 2011 at 10:10, Aroj George <arojis@gmail.com> wrote:
> Yes, the map step is not redone, but I thought the reduce values are cached
> in the internal non-leaf nodes?
> Why then does Couch rerun the reduce every time for the exact same query (
> same group level etc..)

AFAIK, the reduce results are cached in a tree-shaped cache on-disk,
where each member has the reduced results from all its child nodes. If
your query does not exactly match a single parent node, the reduce
query will have to skim a few parent nodes and reduce their results
further (i.e. with rereduce=True). This certainly doesn't mean that
each reduce query will have to calculate the full results from
reducing all the map results, though.

Cheers,

Dirkjan