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Sites Rejecting Apache 2?
An anonymous reader writes "Vnunet
reports on the low adoption of Apache 2 has caused its producers to advocate freezing development of the open-source Web server until makers of add-in software catch up. Almost six months after the launch of Apache 2, less than one percent of sites use it, due to a lack of suitable third-party modules." I'm not sure where they are getting the freezing Apache development part, more talk about forking for 2.1 right now on the httpd mailing list. The article does have it right though that until there is a reason to upgrade and the modules are in place that adoption is not going to happen. While the cores of both Perl and PHP are thread-safe, the third-party modules are not. This renders one the larger reasons to use Apache 2.0, the threaded http support, useless for applications using either of these application layers. It comes down to the question of whether the third-party module writers are better off supporting what is used or what is new.
My main question is, what would it matter if sites weren't using apache 2.0, isn't it enough that open source software is being used??
Ignore the "p2p is theft" trolls, they're just uninformed
Here's what would convince me to change.
... its always nice to know that the big boys have taken the plunge.
.. given that I bothered reading up on some of the early discussions.
-- References. Have any high profile apache sites migrated? While my sites are small
-- PHP Support. As of 4.2.0, Apache2 support was experimental. The change log does not show anything which says its supported.
-- Mod_gzip support. This is a big one. Mod_Gzip makes my sites download a extremely fast when users over dialup lines log in. This is true specially for low bandwidth countries in Asia. Mod_gzip support has left me fairly confused
Even with all of this.. I'm not likely to change unless there is a perceptible difference in the load / performance stats on my system during the switch.
The number one problem with Apache 2 is its reliance on threads, and its assumptions about threading models.
This will certainly not win me friends in the "everything should use threads because it's easier to do linear programming than to build a session reentrant state machine" camp, but...
Threads are useful for SMP scalability, but they aren't very useful for much else (I/O interleaving is adequately handled by most network stacks, the I/O interfaces themselves, and the fact that almost all the bytes being mode are being moved from the server to the client: the protocol is very asymmetric, even if you aren't pushing multimedia files). In most cases, threads are a liability.
Under Windows, they introduce data marshalling issues that have to be accounted for in user code -- not just in the modules which implement interpreters for that user code.
Under UNIX, threads are generally a loss, unless there is specific scheduler support for thread group affinity, when threads are running on the same processor. and CPU negaffinity, when there are multiple processors, to ensure that there is maximal usage of computer resources.
If you do the first, then you have the possibility of starvation deadlock for other applications: basically, it's not possible to do it correctly in the scheduler, you have to do it by means of quantum allocation, outside the scheduler. This means a threading approach such as scheduler activations, async call gates, or a similar technique. If you do the second, then you pay a serious penalty in bus bandwidth any time locality spans multiple CPUs -- in other words, it's useless to use SMP, if you have, for example, a shopping cart session that needs to follow a client cookie around.
Overall, this means that you were much better off using session state objects to maintain session state, rather than using threads stacks to do the same job. This is actually pretty obvious for HTTP, in any case, where requests are handled independently as a single request/response pair, and connection persistance isn't generally overloaded to imply session information (you can't do that because of NAT on the clinet side, multiple client connections by a browser on the client side, and server load balancing on the server side, etc.).
Overall, this factors out into threads bringing additional pain for module writers, without any significant performance or other benefit, unless you go SMP, and have a really decent threads and scheduler implementation -- which means you are running a recent IRIX or Solaris, which is a really limited fraction of the total web server market.
Frankly, they would have been a lot better off putting the effort into the management of connection state and MTCP or a similar failover mechanism, and worried about NUMA-based scaling, rather than shared memory multiprocessor with particular threads implementation scaling. The cost for what you get out of the switch is just too high.
-- Terry