Causes httpd processes spiraling out of control with memory usage?

To: "users@xxxxxxxxxxxxxxxx" <users@xxxxxxxxxxxxxxxx>
Subject: Causes httpd processes spiraling out of control with memory usage?
From: "Rose, John B" <jbrose@xxxxxxx>
Date: Mon, 17 Apr 2017 16:13:46 +0000
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Are there some common causes for a single httpd process to use inordinate amounts of RAM?

I have read about one person having a loop in their mod_rewrite rules. If someone hit the particular URL, the offending Rewrite rule would

cause memory consumption to go out of control

Thanks