This tip is for Windows SharePoint Services 2.0/3.0, SharePoint Portal Server 2003 and Microsoft Office SharePoint Server 2007 and may apply to SharePoint Foundation 2010 and SharePoint Server 2010; when running on IIS 6.0 or IIS 7.0/7.5 with the IIS 6 Management Compatibility role services installed.
Knowing when your IIS server’s application pools are recycling can tell you a lot about the health of your SharePoint web front end servers. By default new application pools are set to recycle once per day at a random time between 1:00AM-3:00AM, server time. If an application pool is recycling more often than that, it may be indicative of a problem. To enable event logging of an application pool recycle event; run the following command from an administrative command line. Replace APP POOL NAME with the actual application pool name. If the application pool name has spaces in the name enclose the name in quotes.
After this command is run, each time the specified application pool is recycled because of time, schedule, failover, number of requests, or on demand; the one of the following events will be written to the Event Log: 1074, 1075, 1076, 1077, 1078, 1079, 1080 or 1177.
For more information on application pool recycling settings see the following KB; http://support.microsoft.com/kb/332088.