Re: [RFC PATCH 10/10] gitweb: Show appropriate "Generating..." page when regenerating cache (WIP)

On Mon, Jan 25, 2010 at 02:48:26PM +0100, Jakub Narebski wrote:

Now those patches (mine and J.H. both) make gitweb use locking
(it is IIRC configurable in J.H. patch) to make only one process
generate the page if it is missing from cache, or is stale.  Now
if it is missing, we have to wait until it is generated in full
before being able to show it to client.  While it is possible to
"tee" output (using PerlIO::tee, or Capture::Tiny, or tie like
CGI::Cache) writing it simultaneously to browser and to cache for 
the process that is generating data, it is as far as I understand
it impossible for processes which are waiting for data.  Therefore
the need for "Generating..." page, so the user does not think that
web server hung or something, and is not generating output.

Ah, ok, so the message is there to cover up for a technical problem. ;-)
I didn't quite realize. Then, it would be great to tweak the mechanisms
so that the user does not really have to wait.

So, I wonder about two things:

(i) How often does it happen that two requests for the same page are
received? Has anyone measured it? Or is at least able to make
a minimally educated guess? IOW, isn't this premature optimization?

(ii) Can't the locked gitwebs do the equivalent of tail -f?


P.S.: Again the disclaimer - if this is "too hard", it's better to
accept patches like they are, then improve this later. But perhaps
a better solution would be not to clutter the code by optimizing this
case at all if it's not clear it really matters in the real world.

				Petr "Pasky" Baudis