ok..I found some answer here
like tmp are using the MyISAM format when stored into the HD.
2012/10/18 franco riggi <franco.riggi@stripped>
> I had several time an error like
> Incorrect key file for table '/tmp/#sql_4aa7_1.MYI'; try to repair it
> and I didn't found any really deep info about how MySQL uses and create
> the temporary files.
> In particular I don't have clear
> 1) why the format is MYI whlle we do not use any MyISAM table (I have only
> 2) how can I monitor how their size ( that is not easy because are hidden
> files) . I have a tmp folder which is around 5G but probably it is not
> 3) best suggestion for tmp tuning
> All the best,
|• Temporary files||franco riggi||18 Oct|
| • Re: Temporary files||franco riggi||18 Oct|