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From: Paul Spangler <paul.spangler@ni.com>
Subject: [PATCH 57300] mod_session save optimization
Message-ID: <55D64DA2.8090309@ni.com>
Date: Thu, 20 Aug 2015 16:58:58 -0500
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Hello,

The bug report contains a more detailed explanation of the patch, but 
there are some points I thought might lead to some discussion.

First a quick summary of the issue: mod_session writes out the session 
every request even if there aren't any changes to the data. This makes 
some sense when the session has a max age and the expiry value needs to 
be refreshed. However, there isn't likely to be much benefit in 
repeatedly refreshing the expiry by a few milliseconds, possibly 
generating database traffic each time. This patch proposes a new 
directive to define an interval of time where the expiry doesn't need to 
be refreshed if there are no session data changes.

1. We had a hard time coming up with a name for the directive. The patch 
goes with SessionExpiryUpdateInterval, being the interval of time that 
may pass before updating the expiry value is required. I don't know if 
there are any existing directives with a similar function that we should 
mimic instead.

2. The patch includes a behavior change independent of the new directive 
when using sessions without a max age: if the data hasn't changed, don't 
write out the session. Most noticeably, this means new sessions that 
never get data are discarded without being saved.

3. I wasn't sure how best to add tests for a new directive since the 
test server won't start if the directive is missing. The patch that 
includes the test changes look for the 2.5 version to know the new 
directive is there, and will require a modification if/when the 
directive is back-ported to 2.4 to enable the new tests.

https://bz.apache.org/bugzilla/show_bug.cgi?id=57300

Thanks for your consideration.
-- 
Paul Spangler
LabVIEW R&D
National Instruments