I have a performance issue that I am still trying to track down. We have a relatively beefy server (PowerEedge 2950 of recent vintage) with lotsa RAM, CPU, etc running Moodle 1.9.2 on a LAMP stack with Fedora 9 as the OS.
I've tried to follow the PHP and MySQL tuning tips scattered throughout the forum and also on the Moodle docs site. However, some clients (and myself on occasion) have poor response times on the WAN side. NOt all the time...but sometimes. Long timeouts displaying forum pages, or sometimes even the Front Page.
I've been monitoring via sar and collectl and the server seems to be idling most of the time (low CPU and disk activity, network and RAM = low usage) - yet the problem persists. I've been capturing packets now trying to analyze the conversations and on thing I noticed was that every so often, Moodle throws out ICMP packets. These are blocked at our routers and I see the ICMP packets around the same time that the timeouts are occurring.
Why is Moodle initiating ICMP packets? I'm probably just not familiar enough with the TCP/IP stack..but no one is "pinging " from the server at the time they occur. That...and any other tips to isolate these slow (60+ second) timeouts would be appreciated.