One way to do this would be with a cron job calling a Perl script that generates the charts twice a day and saves them as image files. Then, the web server would only have to serve up static files, without the need of calling a CGI script to get the images.
Hauke D, thank you for that new suggestion, I didn't think that way.
So, all these images with that chart should be saved under the same file name. And that image file will be inserted in html page. When data change, new image will be saved and automatically will become visible in html page after page refreshing or a new visiting? Did I understood well?
It is really extremely simple. The only con is that it can't show data in a table. But really excellent solution and I can use it for that project or something else.