FATAL: erealloc(): Unable to allocate XXX bytes

[ozzyman]

I got tonz of fatal errors like these in error_log:
FATAL: erealloc(): Unable to allocate 245760 bytes
FATAL: erealloc(): Unable to allocate 15360 bytes
FATAL: emalloc(): Unable to allocate 291 bytes

When busy traffic hours memory usage goes up and database crashes.

I searched and found that its because of RlimitCPU and RLimitMEM values. Is it true or something else?
If it is how can I set these values?
In my httpd configuration goes like these:
RLimitMEM 994982229
RLimitCPU 240