Is it the server.log file? If so, then you control the rolling log in server/instance/log4j.xml where instance is the server instance - most likely default.
The setting is controlled in this section:
<!-- Rollover at midnight each day -->
<param name="DatePattern" value="'.'yyyy-MM-dd"/>
<!-- Rollover at the top of each hour
<param name="DatePattern" value="'.'yyyy-MM-dd-HH"/>
<!-- The default pattern: Date Priority [Category] Message\n -->
<!-- The full pattern: Date MS Priority [Category] (Thread:NDC) Message\n
Just change the threshold value.
Ah, thank you! What went "wrong" is that the treshold parameter was missing for the log file, and hence I missed it. Adding it solved my issue.
Thanks again: loading time is down by over half a minute, and I doubt I would have found it myself for this long-overdue project.