[erlang-questions] Extremely poor Mnesia performance

Edwin Fine <>
Tue Sep 30 18:47:49 CEST 2008


Is it possible to denormalize the data so that you don't have so many
tables? Mnesia can behave as a hierarchical database because you can store
arbitrarily complex terms, including what amounts to trees (lists of tuples
of lists of.....). If your queries are likely to remain the same over time
and you don't need ad-hoc queries, could you consider this approach? The
problem with any hierarchy, of course, is that if you get it wrong it can be
hell on wheels to fix.

On Tue, Sep 30, 2008 at 12:23 PM, <> wrote:

> Thanks Taavi,
>
> That wasn't the answer I was looking for! :-D
>
> Oh dear, well that leaves my plan for using Mnesia in tatters.
>
> I actually need an in memory db which at least has the core subset of RDBMS
> features. So I am essentially just looking for a small in memory DB for
> real-time access.
>
> Has anyone here had any experience using something like KDB with Erlang?
>
> Perhaps I could switch to using KDB as an alternative?
>
> Many Thanks,
> Dan
>
> -----Original Message-----
> From: Taavi Talvik [mailto:]
> Sent: 30 September 2008 17:19
> To: RUBINO, Dana, GBM
> Cc: 
> Subject: Re: [erlang-questions] Extremely poor Mnesia performance
>
>
> On Sep 30, 2008, at 5:58 PM, <> wrote:
>
> >
> > Hey all,
> >
> > I am doing some benchmarking with Mnesia at the moment and am pretty
> > disappointed to say the least.
> >
> > I'm hoping I am doing something wrong.
> >
> > Running a 5 table join below: (two of the tables have ~50k rows the
> > rest a couple of hundred)
>
> Probably you are not doing anything wrong. From mnesia introduction (
> http://www.erlang.org/doc/apps/mnesia/
> Mnesia_chap1.html#1<http://www.erlang.org/doc/apps/mnesia/Mnesia_chap1.html#1>
> ),
> it design goals are:
> ===
> In telecommunications applications there are different needs from the
> features provided by traditional DBMSs. The applications now implemented in
> the Erlang language need a mixture of a broad range of features, which
> generally are not satisfied by traditional DBMSs.
> Mnesia is designed with requirements like the following in mind:
>
>        * Fast real-time key/value lookup
>        * Complicated non real-time queries mainly for operation and
> maintenance
>        * Distributed data due to distributed applications
>        * High fault tolerance
>        * Dynamic re-configuration
>        * Complex objects
> ===
>
> Mnesia is not designed as replacement for relational database. It is
> optimised for fast key-value lookup and distribution.
>
> With qlc:info(Qh) you can get more information, how query is actually
> handled.
>
> best regards,
> taavi
>
>
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