In the last few months we migrated our web application from Tomcat 7.0.55 to 
Tomcat 9.0.19 (26). That transition was relatively straightforward until we 
reviewed the results of our performance tests. Those tests showed an increase 
in CPU usage and disk I/O on our Windows 2012 server. When we switch back to 
Tomcat 7, the metrics for CPU/disk usage were significantly lower (similar to 
previous tests).

As we investigated the cause of the increase in cpu/disk usage we found the 
tomcat process was repeatedly opening and closing the jars of our web 
application. The process profile showed all the jars in WEB-INF/lib being 
closed and reopened within seconds while the application was processing 
requests (and to some extent when quite). Now we are trying to determine why.

We have a general understanding that the 
implementation changed in Tomcat 8.5. The Tomcat 7 implementation provided for 
the configuration of  jarOpenInterval (which we used the default = 90s). The 
latest implementation appears to track the jar modification times with a hash 
map called jarModificationTimes, but we are unable to find a similar 
time-to-live configuration or what triggers the lifecycle listener to close the 
jars (what calls WebappClassLoaderBase.modified() or destroy()) - assuming we 
understand this lifecycle behavior.

The server is configured mostly with default settings. The Context reloadable 
property is NOT set. We have tried increasing the cache time of the Resources 
cacheTtl property as the default of 5s seemed close to the time the jars were 
reloaded. We have not been successful.

What is the cause of the repeated reloading of our web application jars? What 
can trigger the class loader to close all the file handles related to the jars 
in the web application WEB-INF/lib directory - and then open them again within 
a few seconds?

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