On Tue, 5 Sep 2000, Michael Peppler wrote:
> I've come across a technique that allows modperl processes to share a
> pool of database handles. It's not something that I have seen
> documented, so I figured I'd throw it out here.
>
> The idea is to create a pool of connections during the main
> apache/modperl startup. Because these connections end up in the code
> segment for the child processes they are completely shareable. You
> populate a hash in a BEGIN block with x connections, and then provide
> some calls to grab the first available one (I use IPC::Semaphore to
> coordinate access to each connection).
People have suggested this before on the mod_perl list and the objection
raised was that this will fail for the same reason it fails to open a
filehandle in the parent process and then use it from all the children.
Basically, it becomes unshared at some point and even if they don't do
things simultaneously one process will leave the socket in a state that
the other doesn't expect and cause problems. You can cause pages to
become unshared in perl just by reading a variable, so it's almost certain
to happen sooner or later.
Can you try this some more and maybe throw some artificial loads against
it to look for possible problems? It would be cool if this worked, but
I'm very skeptical until I see it handle higher concurrency without any
problems.
- Perrin
