[erlang-questions] mnesia:transform_table

Wed May 26 18:56:06 CEST 2010

Well, seeing as how I don't think the number of columns will get out of hand for me that is certainly enough of a reason to use proplists instead. Thank you.

> From: igorrs@REDACTED
> Date: Wed, 26 May 2010 13:42:46 -0300
> To: silent_vendetta@REDACTED
> CC: erlang-questions@REDACTED
> Subject: Re: [erlang-questions] mnesia:transform_table
> 
> Since a dict consumes more space, the advantage of the proplist is the
> size. Basically, the dict will give you a performance gain that's
> irrelevant (unless you have many columns) and use more space.
> 
> For example:
> 
> 1> List = [{"firstname", "Igor"}, {"lastname", "Sucupira"}, {"gender",
> "male"}, {"birthdate", "02/15/1981"}].
> [{"firstname","Igor"},
>  {"lastname","Sucupira"},
>  {"gender","male"},
>  {"birthdate","02/15/1981"}]
> 2> Dict= dict:from_list(List).
> {dict,4,16,16,8,80,48,
>       {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
>       {{[["lastname",83,117,99,117,112,105,114,97],
>          ["gender",109,97,108,101]],
>         [],
>         [["birthdate",48,50,47,49,53,47,49,57,56,49]],
>         [],[],[],[],[],[],[],[],[],
>         [["firstname",73,103,111,114]],
>         [],[],[]}}}
> 3> GB = gb_trees:from_orddict(orddict:from_list(List)).
> {4,
>  {"gender","male",
>   {"firstname","Igor",{"birthdate","02/15/1981",nil,nil},nil},
>   {"lastname","Sucupira",nil,nil}}}
> 
> 4> erlang:byte_size(term_to_binary(List)).
> 97
> 5> erlang:byte_size(term_to_binary(Dict)).
> 195
> 6> erlang:byte_size(term_to_binary(GB)).
> 125
> 
> 8> timer:tc(lists, keysearch, ["firstname", 1, List]).
> {2,{value,{"firstname","Igor"}}}
> 9> timer:tc(gb_trees, lookup, ["firstname", GB]).
> {3,{value,"Igor"}}
> 10> timer:tc(dict, find, ["firstname", Dict]).
> {4,{ok,"Igor"}}
> 11> timer:tc(lists, keysearch, ["firstname", 1, List]).
> {3,{value,{"firstname","Igor"}}}
> 12> timer:tc(gb_trees, lookup, ["firstname", GB]).
> {3,{value,"Igor"}}
> 13> timer:tc(dict, find, ["firstname", Dict]).
> {4,{ok,"Igor"}}
> 
> 
> On Wed, May 26, 2010 at 1:15 PM, Chris Hicks
> <silent_vendetta@REDACTED> wrote:
> >
> > What do you see as the advantage of Proplist over a Dict though?
> >
> >> From: igorrs@REDACTED
> >> Date: Wed, 26 May 2010 12:48:21 -0300
> >> To: silent_vendetta@REDACTED
> >> CC: erlang-questions@REDACTED
> >> 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
> >> <silent_vendetta@REDACTED> 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: igorrs@REDACTED
> >> >> Date: Wed, 26 May 2010 03:52:23 -0300
> >> >> To: silent_vendetta@REDACTED
> >> >> CC: erlang-questions@REDACTED
> >> >> 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
> >> >> <silent_vendetta@REDACTED> 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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> 
> 
> -- 
> "The secret of joy in work is contained in one word - excellence. To
> know how to do something well is to enjoy it." - Pearl S. Buck.
> 
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