Re: [Erlangweb-users] implementation of edict

[Michal S. <mi...@er...>]

Hi,
Thank you for your email. Both patches should be included in the 1.1  
release, which we are working on right now.

Thanks,
Michal

-- 
Michal Slaski
http://www.erlang-consulting.com

On 30 Aug 2008, at 17:19, Ulf Wiger wrote:

> Just thought I'd think out loud about the implementation of edict.
> Note that I've just been browsing the code on the web, so this
> is just from a quick read-through.
>
> The data representation seems a bit inefficient. For example:
>
>    fset(Key, Value) ->
>    	case ets:lookup(?MODULE, self()) of
>    		[{_, Dict}] -> ets:insert(?MODULE, {self(), dict:store(Key,  
> Value, Dict)});
>    		[]          -> exit(no_dict_attached)
>    	end.
>
> This strategy obviously scales very poorly if a large number of keys
> is inserted.
>
> An alternative strategy would be:
>
> fset(Key, Value) ->
>    case ets:member(?MODULE, self()} of
>       true ->
>          ets:insert(?MODULE, {{self(),Key}, Value});
>       false ->
>          exit(no_dict_attached)
>    end.
>
> ...and so on.
>
> The penalty will be incurred on terminate_state(), which will
> look something like this:
>
> terminate_state() ->
>    ets:delete(?MODULE, self()),
>    ets:match_delete(?MODULE, {self(),'_'},'_'}).
>
> (the ets table being an ordered_set, of course.)
>
>
> Since it would appear as if this module will be called many times  
> while
> building a page, I would think that this ought to give better  
> characteristics.
>
>
> One more thing - I believe this function to be wrong:
>
> fset(List, Key, Value) ->
> 	case ets:lookup(?MODULE, self()) of
> 		[{_, Dict}] -> ets:insert(?MODULE, {self(), dict:store(List, [{Key,
> Value}|dict_fetch(List, Dict)], Dict)});
> 		[]          -> exit(no_dict_attached)
> 	end.
>
>
> The dict_fetch/2 function returns 'undefined' if there is no occurence
> of the key List.
> That would mean that calling e.g. fset("list", "person", "john")
> before storing an
> initial value for "list", would result in the term {"list",
> [{"person","john"}|undefined]}
> in the dictionary. It would be better to return an error or initialize
> it to [] first.
>
> BR,
> Ulf W
>
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