Mod_evasive Doesn't Protect From Apache DOS

We tried to use one software for offline browsing to download our site and test it if it will fail or not. We used 500 threads at once. Program was able to request 56 pages per second. Of course server (site) failed because there were no more available mysql connections. So site went down. Mod_evasive didn't block that.

Here is the config:

<IfModule mod_evasive20.c>
DOSHashTableSize 3097
DOSPageCount 2
DOSSiteCount 80
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 30
DOSLogDir "/var/log/httpd"
</IfModule>

Here is the copy of text I found on one site about mod_evasive:

Mod_evasive does work relatively well for small to medium sized brute force or HTTP level DoS attacks. There is, however, an important limitation that mod_evasive has that you should be aware of. The mod_evasive module is not as good as it could be because it does not use shared memory in Apache to keep information about previous requests persistent. Instead, the information is kept with each child process or thread. Other Apache children that are then spawned know nothing about abuse against one of them. When a child serves the maximum number of requests and dies, the DoS information goes with it. So, what does this mean? This means that if an attacker sends their HTTP DoS requests and they do not use HTTP Keep-Alives, then Apache will spawn a new child process for every request and it will never trigger the mod_evasive thresholds. This is not good…

Is there any solution for such type of attack with Keep Alive disabled?