Bug 47180 - DBM ssl_scache setting can cause extreme performance degradation
Summary: DBM ssl_scache setting can cause extreme performance degradation
Alias: None
Product: Apache httpd-2
Classification: Unclassified
Component: mod_ssl (show other bugs)
Version: 2.2.11
Hardware: Sun Solaris
: P2 normal (vote)
Target Milestone: ---
Assignee: Apache HTTPD Bugs Mailing List
Keywords: MassUpdate
Depends on:
Reported: 2009-05-11 01:50 UTC by Mick Sheppard
Modified: 2018-11-07 21:09 UTC (History)
0 users


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Description Mick Sheppard 2009-05-11 01:50:29 UTC
We are running Apache 2.2 on Solaris 10 with the following SSL cache settings:-

SSLSessionCache         dbm:/usr/local/apache2/logs/ssl_scache
SSLSessionCacheTimeout  300

We have connections from clients using client certificates for authentication. These connections are programs rather than interactive. As such each connection exists for a single discrete request.

The session cache is checked each SSLSessionCacheTimeout seconds for expired SSL session information. This is performed by all httpd processes independently. This check consists of at least one sequential search of the DBM file. During this all other SSL operations are blocked.

We have seen that under load the size of the DBM file grow to between 1 and 2 GB. As the file grows in size it takes longer to traverse it and the server suffers intermittent performance issues. Once the time to traverse the file exceeds the SSLSessionCacheTimeout the server responds to requests at the rate of one per SSLSessionCacheTimeout.

It is possible to workaround this by disabling the session cache or changing to use shared memory.
Comment 1 William A. Rowe Jr. 2018-11-07 21:09:45 UTC
Please help us to refine our list of open and current defects; this is a mass update of old and inactive Bugzilla reports which reflect user error, already resolved defects, and still-existing defects in httpd.

As repeatedly announced, the Apache HTTP Server Project has discontinued all development and patch review of the 2.2.x series of releases. The final release 2.2.34 was published in July 2017, and no further evaluation of bug reports or security risks will be considered or published for 2.2.x releases. All reports older than 2.4.x have been updated to status RESOLVED/LATER; no further action is expected unless the report still applies to a current version of httpd.

If your report represented a question or confusion about how to use an httpd feature, an unexpected server behavior, problems building or installing httpd, or working with an external component (a third party module, browser etc.) we ask you to start by bringing your question to the User Support and Discussion mailing list, see [https://httpd.apache.org/lists.html#http-users] for details. Include a link to this Bugzilla report for completeness with your question.

If your report was clearly a defect in httpd or a feature request, we ask that you retest using a modern httpd release (2.4.33 or later) released in the past year. If it can be reproduced, please reopen this bug and change the Version field above to the httpd version you have reconfirmed with.

Your help in identifying defects or enhancements still applicable to the current httpd server software release is greatly appreciated.