Red Hat Bugzilla – Bug 493458
Last modified: 2010-06-28 07:38:37 EDT
mod_mem_cache has disappeared from rawhide apache (httpd-2.2.11-8.x86_64), without any hint of a reason
a) because nobody should be using it
b) to find out if anybody was using it, and if so, why
So - are you using it? if so... why?
I'm using it because it's a cheap way to set up a caching proxy on a system where apache is already deployed. I need a local proxy to speed up mock.
Let me rephrase:
Why are you using mod_mem_cache in favour of mod_disk_cache?
Because memory is cheap and fast ?
I have a two-tiers proxy setup : persistent disk cache for big files (typically rpms) and mem cache for the rest
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.
More information and reason for this action is here:
If for no other reason than the apache httpd gods have it as an option and it is listed in their docs as an option. Are you a httpd committer? Who made you god of apache httpd to make such a decision? If it is UP stream and you do not think it is necessary, SO WHAT?! Let people make their own decision and not load it. Print out a BIG notice "I don't think you should use this module" or something like that, but come on!
My concern is that people are not making informed decisions.
I don't think it would be controversial to state that there is a rough consensus upstream that mod_disk_cache outperforms mod_mem_cache, and that the latter is redundant and buggy. The simple argument that RAM is "faster" than disk, therefore mod_mem_cache is "better", does not hold water, because the kernel buffer cache will use available RAM to cache disk content anyway.
Certainly, I've not heard anybody claim to be using mod_file_cache.
Joe is a longtime maintainer of this package in Fedora. I do think that it would have been good to put a release note into the Web Servers beat. This change came as a small (but very manageable) surprise to the Websites team, which had to change some configuration and directions for contributors working on mockups or development of our fedoraproject.org sites.
And I should point out in fairness that, having seen this change myself at the time, as part of helping Websites, I could have done that just as easily and it didn't occur to me at the time. Apologies.
(In reply to comment #7)
> My concern is that people are not making informed decisions.
> The simple argument that RAM is "faster" than
> disk, therefore mod_mem_cache is "better", does not hold water, because the
> kernel buffer cache will use available RAM to cache disk content anyway.
You still need to hit the disk first. That may not be a concern for dedicated proxy systems, but it is for everyone with a light proxy use on a system that does all kinds of other things with disks that may not be speed daemons.
Joe, your argument in #7 is valid and correct, but irrelevant.
The application API, or functionality was changed just because you thought it was correct. So what?! That just causes grief to users who expect to maintain a certain stability between releases and with official documentation. That it was changed JUST for fedora is my complaint.
w.r.t. comment 10: you can also run mod_disk_cache on a tmpfs mount. This will work much better than mod_mem_cache.
w.r.t. comment 11: I am sorry that I forgot to relnote this, that was an oversight. The set of modules we choose to ship and support in Fedora is a decision made in Fedora alone, not upstream.
Really: I am still looking for motivation to add these modules back. If anybody will present a coherent argument, performance numbers, list of bugs which are present in mod_disk_cache but not mod_mem_cache, etc, I will add them back. But I'm not seeing that.
It is a waste of time and resources to ship and support modules which are functionally equivalent, but inferior in implementation, to the recommended set; I also consider it irresponsible, since people can be, and are, duped into using these modules and thereby needlessly exposed to their bugs.
It appears that mod_disk_cache is also no longer provided. Is there an alternative to that which should be used?
mod_disk_cache is still provided.
Also worth noting that mod_mem_cache has been removed from upstream trunk.
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