[erlang-questions] Index Overhead In Mnesia

Ben Hood <>
Tue Jun 10 18:06:00 CEST 2008


On Tue, Jun 10, 2008 at 4:30 PM, Hynek Vychodil
<> wrote:
> I think this is feature of bag and duplicate_bag ets table types and is
> mentioned in manual.

Maybe, but my table does not specify a type, so it be a set by default.

According to the mnesia manual, the three types of table are set,
ordered_set or bag, whereas in ets/dets you can have a duplicate_bag
as well.

In the mnesia man page it states:

"Indices do not come free, they occupy space which is proportional to
the size of the table. They also cause insertions into the table to
execute slightly slower."

But I can't see anything specific about using bags and indices.

I googled this post by Ulf a few years ago, which may shed some light
onto the situation:


There seems to be a reference to a (now unmaintained) version of a
mnesia index, which I assume to be the rdbms module in jungerl.

Does anybody know if that addresses the issue, or even exactly what
the underlying problem is?


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