When looking at a webserver for memory usage, it’s important to consider the VSZ and RSS memory usage.

This little one liner gets the Total and Average VSZ and RSS usage as well as thread count, and prints those statistics every 5 seconds:

# while true; do ps auxfww | grep apache | grep -v -e cronolog -e grep | awk '{ vsum+=$5; rsum+=$6 } END { print "VSZ:", vsum, "(", vsum/NR, ") RSS:", rsum, "(", rsum/NR, ") Procs:", NR }'; sleep 5; done;
VSZ: 9896272 ( 341251 ) RSS: 1716216 ( 59179.9 ) Procs: 29
VSZ: 9547608 ( 340986 ) RSS: 1650100 ( 58932.1 ) Procs: 28
VSZ: 9546328 ( 340940 ) RSS: 1649044 ( 58894.4 ) Procs: 28
VSZ: 9861976 ( 340068 ) RSS: 1687968 ( 58205.8 ) Procs: 29
VSZ: 9868632 ( 340298 ) RSS: 1694496 ( 58430.9 ) Procs: 29
VSZ: 9853272 ( 339768 ) RSS: 1679112 ( 57900.4 ) Procs: 29
VSZ: 9853272 ( 339768 ) RSS: 1679264 ( 57905.7 ) Procs: 29
^C
#

So there are around 29 threads running right now on this server. The threads are using an average of 340MB per thread VSZ, and 59MB per thread RSS. The total of around 1.7GB of RSS looks good, on a machine with 8G physical memory.