If you have tried to use Apache 2.4.x you have probably run into this bug and seen your error log filled with
[proxy_balancer:emerg] [pid 3632:tid 428] (22)Invalid argument: AH01186: worker slotmem_grab failed
AH00020: Configuration Failed
The bug 52402 has a patch attached that Mario has tested and said to fix the issue. So, since it was asked on the Apache Lounge, I thought I'd make a patched mod_proxy_balancer module.
If you wish, feel free to give it a try
Download Link Removed
Fixed in Apache 2.4.3, just upgrade your Apache