[erlang-questions] Extremely poor Mnesia performance

Dana.RUBINO <>
Tue Sep 30 18:23:46 CEST 2008


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),
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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