Re: HTTP and MPM support

On Fri, Jan 25, 2019 at 11:35 AM John Dunlap <[email protected]> wrote:

> I'm in the process of optimizing our web application for performance and
> one thing that I was really excited to try was mod_http2 because it allows
> the browser to send multiple requests through the same TCP connection with
> compressed headers. However, when I enabled it and restarted apache I was
> greeted with this:
>
> [Fri Jan 25 12:30:57.813355 2019] [http2:warn] [pid 10186] AH10034: The
> mpm module (prefork.c) is not supported by mod_http2. The mpm determines
> how things are processed in your server. HTTP/2 has more demands in this
> regard and the currently selected mpm will just not do. This is an advisory
> warning. Your server will continue to work, but the HTTP/2 protocol will be
> inactive.
>

To this question, the answer should be blatantly obvious; http2 doesn't
simply support multiple requests (connection: keepalive solved that)
but supports parallel requests. This clearly isn't compatible with any
single-threaded/single-worker per connection strategy.

A hybrid mod_prefork could be coded to dispatch all worker requests
across to distinct worker processes for a single connection, but I
don't anticipate anyone interested in doing such development.


> The last time I tried to use either mpm_worker or mpm_event my application
> was plagued by seemingly random segfaults. Are there any plans to support
> other MPM's? If not, the benefits of HTTP2 appear to be permanently out of
> reach for our mod_perl applications and that, honestly, might force us into
> seriously reevaluating our technology stack. :(
>

Your compatibility with the worker MPM is likely much stronger than
with the event MPM; however... all request workers can behave in a
"free threaded" manner under mod_http2, eliminating the relative
simplicity of the worker MPM. Working out each and any of these
specific segfaults occurs is the only way to improve the situation.

For the general mod_perl activity to increase, the Apache Perl Project
needs active volunteers and contributions. Consider this entire thread
an open invitation to participate.