[erlang-questions] mnesia:transform_table

Chris Hicks <>
Wed May 26 18:15:17 CEST 2010


What do you see as the advantage of Proplist over a Dict though?

> From: 
> Date: Wed, 26 May 2010 12:48:21 -0300
> To: 
> CC: 
> Subject: Re: [erlang-questions] mnesia:transform_table
> 
> I thought of using a dict or a gb_trees to store the fields of each
> entry, but I gave up in seconds (;-)), because the only advantage
> (compared to proplists) would be the speed to retrieve a field (what
> is very fast, anyway), once you have read the record from the database
> (which is the slowest part).
> Considering that the performance difference to find a field is not
> significant if the number of fields is not big, using a gb_trees would
> be just a waste of space, for the huge majority of the cases.
> 
> On Wed, May 26, 2010 at 12:08 PM, Chris Hicks
> <> wrote:
> >
> > Yes I am still modeling tables and I remembered reading your blog, I'm just making sure I understand all of my options beforehand. I'm trying to decide between using a list with key-value pairs, a dict and a proplist. Are there any major disadvantages to using one of those over the other?
> >
> >> From: 
> >> Date: Wed, 26 May 2010 03:52:23 -0300
> >> To: 
> >> CC: 
> >> Subject: Re: [erlang-questions] mnesia:transform_table
> >>
> >> If you are still modelling the tables, you might also want to consider
> >> some approach to avoid running mnesia:transform_table/3, since it
> >> needs to rewrite all the records.
> >>
> >> For example, as described here:
> >> http://igorrs.blogspot.com/2010/05/mnesia-one-year-later-part-2.html#key_value
> >>
> >> And discussed in this thread (from the third post on):
> >> http://forum.trapexit.org/viewtopic.php?p=55510&sid=cc3aec96ba9387b61b5d192ccd1de1a6
> >>
> >> Good luck.
> >> Igor.
> >>
> >> On Wed, May 26, 2010 at 2:09 AM, Chris Hicks
> >> <> wrote:
> >> >
> >> > So when updating a record definition the updated record, when reloaded, is not compatible with the old version of the record, as far as I understand it. Updating a Mnesia table to handle the new definition is straightforward enough but, my question revolves around the rest of the running system. Mainly I want to know what is the general (if there is one) process to updating a running system in this manner?
> >> > Should you create a function which locks the whole table, reloads the code and updated all the definitions at the same time? What happens to the rest of the running system when you update a record definition while a process is in the middle of working with that old record?
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> 
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> know how to do something well is to enjoy it." - Pearl S. Buck.
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