https://bz.apache.org/bugzilla/show_bug.cgi?id=69617
Bug ID: 69617
Summary: Add a reminder about potential high heap memory usage
in description of maxHttpRequestHeaderSize
Product: Tomcat 10
Version: unspecified
Hardware: PC
OS: Mac OS X 10.1
Status: NEW
Severity: enhancement
Priority: P2
Component: Documentation
Assignee: dev@tomcat.apache.org
Reporter: maggie.zhan...@sap.com
Target Milestone: ------
If the description of maxHttpRequestHeaderSize could be enhanced to indicate
the potential for high heap memory usage when setting the value too large, it
would be helpful.
In our service, we occasionally receive requests with large header information.
To accommodate this, we set max-http-request-header-size to a large value,
around 10MB, assuming that Tomcat would automatically adjust the header buffer
size as needed.
However, we encountered high memory usage issues when handling batch requests
(approximately 600 per minute). Multiple processors were created, each
allocating memory with max size for a byte buffer to store header data — even
when the headers were small. Since these processors are designed for reuse and
are not immediately destroyed, the used heap memory remained high. Over time,
this led to potential OutOfMemory (OOM) errors when new batch requests arrived.
After reviewing the source code, we reduced the setting to a more appropriate
value, which mitigated the issue. It would be greatly beneficial if the
documentation could highlight this potential memory impact. Thank you.
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