[erlang-questions] Index Overhead In Mnesia

Sean Hinde <>
Tue Jun 10 19:03:52 CEST 2008


Hi,

> So, if I understand you correctly, what I conclude is that the index
> performance degrades when you have lots of identical keys.

Yep!

> Do you know why this is the case?
>
> Does the index perhaps maintain a list of values for each key and
> hence the set of values has to be updated continuously?

Yes

> If so, is this a bug or a feature?

It is a long standing "feature" of mnesia secondary indexes. It is one  
that I also ran into a few weeks into my use of Erlang/mnesia.

I guess it is in the same category as repeated queue scanning for  
selective receive - easy to workaround in most cases, so no major  
incentive to change the behaviour.

Sean




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