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From: Jens Alfke <jens@couchbase.com>
To: "user@couchdb.apache.org" <user@couchdb.apache.org>,
	"j.jakobitsch@semantic-web.at" <j.jakobitsch@semantic-web.at>
Date: Mon, 20 May 2013 09:55:13 -0700
Subject: Re: custom index
Thread-Topic: custom index
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On May 20, 2013, at 12:18 AM, J=FCrgen Jakobitsch SWC <j.jakobitsch@semanti=
c-web.at> wrote:

> i need to be able to create a custom index (btree) on
> what was once a table column.=20
> i saw that there's an geo spatial extension which was always a sign of
> custom indizes.
> i need to create a special btree (a regex btree) for a certain key in a
> json document that does some magic.

It depends on how =93custom=94 the index needs to be. As Jonas said, CouchD=
B=92s built-in indexing mechanism is called =93views=94. It=92s fairly flex=
ible =97 your map function can define any JSON value as a key for a documen=
t, and you can later query on specific keys or key ranges. This becomes esp=
ecially powerful if you use arrays as keys, as it lets you set up primary/s=
econdary search criteria.

But views aren=92t all-powerful. Geospatial queries are one example of some=
thing regular views can=92t handle, because they require range tests on mul=
tiple axes at once. That=92s why they had to be added as a custom index typ=
e in CouchDB. I have no knowledge of how custom indexes are added, but I su=
spect it=92s difficult (because it=92s rarely done) and it would definitely=
 require knowledge of Erlang.

Why don=92t you describe your requirements in more detail. A lot of the tim=
e we can come up with a fairly clean way to implement people=92s indexing n=
eeds using regular views =97 they=92re surprisingly powerful.

=97Jens=