What does a slow "Parsing Segment, Embed, and Global Vars Conditionals" log entry mean?

Question

I'm working on getting EE installed on Google Appengine's new PHP runtime.

Things are slow, and I'm trying to identify why that might be. I've disabled most add-ons, and created an EE tag-less template. The url is a straightforward template-group/template format.

It should be really fast, but I'm seeing a very slow stage I've never seen slow before:

(0.030650/1.42MB) - Parse Current Time Variables
(0.030660/1.42MB) - Parsing Segment, Embed, and Global Vars Conditionals 
(0.339330/1.43MB) - - Beginning Tag Processing - 

What exactly happens during that Parsing Segment... stage?

Answer 1

Yes, simple conditionals are parsed in that stage. But also, module and plugin files are "scanned". The first and third party directories are read for the presence of module and plugin files and stored for reference. If you have a lot of add-ons in the 3rd party folder (having them installed is irrelevant here), it might take longer, especially if the server is bad at disk IOs.