[erlang-questions] Extremely poor Mnesia performance

Dana.RUBINO <>
Tue Sep 30 18:52:22 CEST 2008


Hi Edwin,

Thanks and good idea - I am actually investigating that route right this moment!

I think I could definitely do it, the problem being that after an initial bootstrap of the Mnesia tables I will be in a situation where I will be receiving live/real-time updates to the data. These unfortunately will need to be reflected in mnesia so that the queries performed against it are fully up-to-date whilst still enabling real-time response rates to the queries themselves.

A bit of a mouthful I know!

Many Thanks,
Dan

________________________________
From:  [mailto:] On Behalf Of Edwin Fine
Sent: 30 September 2008 17:48
To: RUBINO, Dana, GBM
Cc: ; 
Subject: Re: [erlang-questions] Extremely poor Mnesia performance

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, <<mailto:>> 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:<mailto:>]
Sent: 30 September 2008 17:19
To: RUBINO, Dana, GBM
Cc: <mailto:>
Subject: Re: [erlang-questions] Extremely poor Mnesia performance


On Sep 30, 2008, at 5:58 PM, <<mailto:>> 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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