Az's Link Spam http://www.underhanded.org/blog I'm Bored en Apache Memory Usage http://www.underhanded.org/blog/2008/07/18#apachemem After a day of trying to figure out why one of my web servers was locking up, I found that it was using a bit too much memory. But I had no idea how much, and Linux memory reporting is a bit arcane at best. Especially with something like apache + PHP using shared memory pools. So after some analysis, I came up with the following script: <br><br> <a href="/apachemem.pl.txt">apachemem.pl</a> <br><br> It had the following output: <br><br> <pre> Total memory available: 3.21G Total used by apache2 (451 instances): 3.80G Total used by other processes: 0.12G Average memory used per apache2 process: 8.63M Recommended number of processes based on Average: 381 Needed memory for 500 processes based on Average: 4.21G Max memory used for apache2 process: 17.61M Recommended number of processes based on Max: 186 Needed memory for 500 processes based on Max: 8.60G Mean plus two Standard Deviations (bulk of usage under max): 11.28M Recommended number of processes based on Mean + 2*Stdev: 291 Needed memory for 500 processes based on Mean + 2*Stdev: 5.51G </pre> At the time I ran it, I had 450 instances out of a configured max of 700 active. Come to find out I only had the ram to support about 380 of those at best. :( <br><br> Hopefully some other people find this useful, as it's pretty hard to get a straight answer on "How many processes can I support?" Now if only php and the standard modules would officially work with the worker MPM. Apache Keepalive http://www.underhanded.org/blog/2008/04/30#keepalive So, for the web servers at work, we had disabled Apache's <a href="http://www.underhanded.org/blog?redirectURL=http%3A%2F%2Fhttpd.apache.org%2Fdocs%2F2.2%2Fmod%2Fcore.html%23keepalive" onMouseOver="window.status='http://httpd.apache.org/docs/2.2/mod/core.html#keepalive'; return true;" onMouseOut="window.status=''; return true;" target="_BLANK">KeepAlive</a> settings due to possible denial of service. As part of some performance tuning I had turned it back on with a low timeout (4 seconds) to see how it held up. Here's the results: <br><br> <center><img src="/pics/concurrent.png" alt="Concurrent Connections" /></center> <br><br> The drop on the right is where KeepAlive was turned on. We did need to increase our MaxServers a bit for when load got high, but overall it's resulted in a huge speedup for the servers and less thrashing in general.