[erlang-questions] Mnesia, disk_log and dets

Dawid Figiel <>
Wed Feb 17 11:50:22 CET 2010


Ulf knows probably everything about mnesia, I know it rather as a common user, but your ideas seems to be interesting. I would like to have database with mnesia API, but more efficient and more powerful backend... also more flexible and extend-able. I was playing with Mnesiaex but I've had some issues with dependencies and TC (Tokyo Cabinet) was chosen.
Anyway subject is interesting especially from the efficiency point of view. I'm looking forward to seeing your results :)



Erlang Solutions Ltd, formerly Erlang Training & Consulting Ltd

----- Original Message -----
From: "wde" <>
To: "Ulf Wiger" <>
Cc: "erlang-questions" <>
Sent: Wednesday, February 17, 2010 7:38:11 AM GMT +00:00 GMT Britain, Ireland, Portugal
Subject: Re: Re: [erlang-questions] Mnesia, disk_log and dets

ok thank you.

With Mnesiaex we can have our own storage backend for the  new "external_copies" type. 

But instead of specifying a new copy type, I'm currently trying to understand how I can integrate a wrapper module
like "mnesia_disc_backend" that handle all disc access (for disc_copies and disc_only_copies) , and do the same thing for the "ram_copy" type, by using a "mnesia_ram_backend" module.

The idea is to offer more flexibility and easily change the backend for ram and disc I/O.

Do you think I'm wasting my time or that there is no interest for something like that ?

>wde wrote:
>> hello,
>> I'm reading the source code of Mnesia to understand how things work
>> :+) If I have understood correctly, for "disc_copies" tables, data
>> are written to disc by using the "disk_log" module. For
>> "disc_only_copies" tables, Mnesia uses "dets".
>> What not use the same disk backend ?
>Originally, they did use the same back-end, but it turned out,
>from experimentation, that dumping the entire table using disk_log
>was /much/ faster than writing out the individual changes into
>a dets file.
>Ulf W
>Ulf Wiger
>CTO, Erlang Solutions Ltd, formerly Erlang Training & Consulting Ltd
>Since January 1st 2010 Erlang Training and Consulting Ltd. has become ERLANG SOLUTIONS LTD.

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