[elephant-devel] Re: Duplicate values in PM-BTREE-INDEX

[Ian Eslick]

We don't declare secondary indicies on dup-btrees, in case that wasn't clear...

Sent from my BlackBerry

-----Original Message-----
From: Alex Mizrahi <alex.mizrahi at gmail.com>

Date: Thu, 26 Jun 2008 13:21:02 
To:elephant-devel at common-lisp.net
Subject: [elephant-devel] Re: Duplicate values in PM-BTREE-INDEX


> Why make the index unique when the btree allows duplicates?

in normal btrees keys are unique.
in btrees-with-duplicates key+value pairs are unique.

that's the idea. for normal btrees we create index on keys only, for dup-btrees 
-- index on pairs.

allowing duplicated key+value pairs will totally break the way cursor works, 
because they assume that key+value pair identifies current row. (and perhaps it 
will break some other things, like remove-kv-pair).

it's possible to implement duplicated pairs support, but that's pretty hard, 
and i don't see any practical reason for this.

> This breaks inverted indices with duplicate values.

it does not. value->oid pairs are always unique.


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