[Python-Dev] Idea: more compact, interned string key only dict for namespace.

[INADA Naoki]

> Memory usage
> --------------------
>
> on amd64 arch.
>
> key-sharing dict:
>
> * 96 bytes for ~3 items
> * 128 bytes for 4~5 items.

Note: There are another shared key.

* 128 bytes for ~3 items
* 224 bytes for 4~5 items

So, let S = how many instances shares the key,

* 90 + (96 / S) bytes for ~3 items
* 128 + (224 / S) bytes for 4~5 items

>
> compact dict:
>
> * 224 bytes for ~5 items.
>
> (232 bytes when keep supporting key-shared dict)
>
> interned key only dict:
>
> * 184 bytes for ~5 items
>
>
> Note
> ------
>
> Interned key only dict is still larger than key-shared dict.
>
> But it can be used for more purpose.  It can be used for interning string
> for example.  It can be used to kwargs dict when all keys are interned already.
>
> If we provide _PyDict_NewForNamespace to extension modules,
> json decoder can have option to use this, too.
>
>
> --
> INADA Naoki  <songofacandy at gmail.com>



-- 
INADA Naoki  <songofacandy at gmail.com>