Backend performance, frontend performance
Well Since you are on 4.0 if possible I would recomend to take it up to 4.1, 4.2, 4.3,4.4 and then to 5.0 (you might skip some steps but you have to look in the release documents which update is possible from what version)
I know it like someone asking that windows XP crashes a lot and I give the advice to update to Windows 7 - so please forgive me.
If you don't want to, or can't update then I would look for the following first aid steps
1) Debug set to false in web.config
2) Site is warmed up
3) Compression GZIP on for dynamic and static content
4) Site is optimized.
- Don't leave JPEG compression to SF but do it outside Photoshop and have images in various sizes
- Remove all unneeded CSS (stylebuilder adds a lot of stuff)
- Optmize CSS http://www.minifycss.com/css-compressor/ and pack if possible multiple stylesheets into one (less requests on server)
5) try turning script combining off this could help
6) add more RAM to the server. Yes hardware makes a difference
Once you have done all of this we sure will think of more in the forum :-)
4.0 is just a very very very early release of the new SF and updating might be the right way to go (a pain, a lot of work and hassle) but might be worth it in the end because in one year support will be hard for 4.0 anyhow. Its like asking a window 95 question.
PS: Wild guess on your sreenshot is that the communication between your site and SQL DB is off somehow. But that's only a 1% guess.
Hello Markus Berchtold
Thank you for reply. I have already set debug mode -> false, server's RAM is good enough, scripts combining is off(yes, i know, it was your suggestion, too. But didn't help). And i've just been compressed (Compression Ratio: 22.6%) my CssClasses. It helps a little bit. By the way, could you give me SQL query to truncate revision history tables, if you know(I found queries like that, but they are for earliest SF versions). If it wont help, I have only one way to get speed - to take SF up to 4.4 or 5.0.
Thank's for the feedback. I really would backup your DB and site and go through the hassle of updating. Again you CANNOT move from 4.0 to 4.4 or 5.0 directly. You need some steps in between.
Can your site be accessed on the web to have a look at the front-end?