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Posted to bugs@httpd.apache.org by bu...@apache.org on 2007/05/15 18:25:43 UTC
DO NOT REPLY [Bug 42425] New: - Additional freshness checks in mod_cache.c cause must-revalidate or max-age=0 content to not get stored.
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Summary: Additional freshness checks in mod_cache.c cause must-
revalidate or max-age=0 content to not get stored.
Product: Apache httpd-2
Version: 2.3-HEAD
Platform: All
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: mod_cache
AssignedTo: bugs@httpd.apache.org
ReportedBy: basam@stream.aol.net
Here is the relevant output from diff of the 2.2.3 from the 2.2.4 version of
mod_cache.c
diff httpd-2.2.3/modules/cache/mod_cache.c httpd-2.2.4/modules/cache/mod_cache.c
428a431,435
> else if (exp != APR_DATE_BAD && exp < r->request_time)
> {
> /* if a Expires header is in the past, don't cache it */
> reason = "Expires header already expired, not cacheable";
> }
The above check is comparing the the expires time from the server (in second
granularity) to the request_time from the client ( upto micro second
granularity). Even though we have all of our hosts running NTP, it is possible
to get a very small skew which is enough to cause this check to pass and the
object ends up not getting put into local cache.
We have a workaround by commenting out the above code, but i don't believe this
check is needed when you have an explicit expires or Cache-Control header from
the server.
regards,
Sridhar
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DO NOT REPLY [Bug 42425] - Additional freshness checks in mod_cache.c cause must-revalidate or max-age=0 content to not get stored.
Posted by bu...@apache.org.
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------- Additional Comments From basam@stream.aol.net 2007-05-15 13:47 -------
Some of the content we server is required to have an expires "now" or max-age=0
or must-revalidate to guarantee freshness.
Without this check, the origin sees IMS requests from the cache a vast majority
of the time so isn't being taxed that much.
With the additional check, the edge does a lot more unconditional GET requests
to the origin taxing the origin resources a lot more.
regards,
Sridhar
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DO NOT REPLY [Bug 42425] - Additional freshness checks in mod_cache.c cause must-revalidate or max-age=0 content to not get stored.
Posted by bu...@apache.org.
DO NOT REPLY TO THIS EMAIL, BUT PLEASE POST YOUR BUG�
RELATED COMMENTS THROUGH THE WEB INTERFACE AVAILABLE AT
<http://issues.apache.org/bugzilla/show_bug.cgi?id=42425>.
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INSERTED IN THE BUG DATABASE.
http://issues.apache.org/bugzilla/show_bug.cgi?id=42425
rpluem@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |NEEDINFO
------- Additional Comments From rpluem@apache.org 2007-05-15 13:08 -------
I do not get your problem here. Caching is only denied if there is an Expires
header and if the time mentioned in the Expires header is earlier then the
request time. If this comparison becomes true only due to the different
granularity of the times measured (which can happen) this means that the
difference between the time in the Expires header and the request time is less
than a second. So there is a very short period of time (less than a second)
during which this entity (if it is cached) would be regarded as fresh and thus
deliverable to the client from the cache without further revalidation. So what
is the point in having cached objects that are that short lived?
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