ets traversal time

Jim Morris <>
Thu Jul 16 02:11:17 CEST 2009


Have you tried ets:foldl which is tail recursive (presumably as it
does not specify in the docs, but it is in lists:foldl) or is there a
reason to use foldr?

If foldr is not tail recursive then I suspect that with 20K entries
the stack will get used up and or eat a lot of memory which needs to
be allocated and released, maybe even causing swapping to the disk.


On Jul 15, 7:53 am, Joel Reymont <> wrote:
> I have a table with 20k entries that I'm traversing like this:
>
>      Msg1 = {message, iolist_to_binary(mochijson2:encode(JSON))},
>      F = fun({Pid, _}, _) -> Pid ! Msg1 end,
>      F1 = fun() ->
>                   A = now(),
>                   ets:foldr(F, ignore, State#state.subs),
>                   io:format("time: ~p~n", [timer:now_diff(now(), A) /  
> 1000])
>           end,
>      spawn_link(F1),
>
> It takes me twice as long to traverse the table the second time around.
>
> Any suggestions as to why and how to fix this?
>
>         Thanks, Joel
>
> --
> Case #1
>
> info: [{memory,283357},
>         {owner,<0.763.0>},
>         {heir,none},
>         {name,subs},
>         {size,20000},
>         {node,''},
>         {named_table,false},
>         {type,set},
>         {keypos,1},
>         {protection,protected}]
> time: 1050.958ms
>
> Case #2
> info: [{memory,283357},
>         {owner,<0.763.0>},
>         {heir,none},
>         {name,subs},
>         {size,20000},
>         {node,''},
>         {named_table,false},
>         {type,set},
>         {keypos,1},
>         {protection,protected}]
> time: 2076.814ms
>
> ---
> Mac hacker with a performance benthttp://www.linkedin.com/in/joelreymont
>
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