Good to know other people want to share about successful scaling with PHP.
On the downside, I have a book cooking on the same exact subject, with release planned September (self-publish, about 80% done), but now not sure if it's worth continuing.
[edit]Slight moment of "panic", as seeing someone else releasing a book on the same subject made me sad, but you're right, no reason not to continue.
Just because one person releases a book doesn't mean you don't have something valuable to share as well. I say go for it. There's bound to be a lot of stuff in your book this one misses, and probably vice versa. People who are facing large-scale situations generally want all the information they can get their hands on.
If you need to know PHP scaling, a) the amount of money that two books cost is still absolutely meaningless to you, b) you will, very probably, still have questions after thoroughly reading your first book and c) it is worth having a second book just to have a second shot at book cover art which will convince one of your engineers to actually read the damn thing instead of re-inventing it poorly as need arises.
Absolutely finish and release your book. Half-writing a book is an even worse decision than writing a book. (Tongue only somewhat in cheek there: if you have actionable information on how to scale PHP, a book is one of the worse ways to change people's lives with that information while simultaneously making money from it.)
At my first company, I freaked when we got a major competitor. The CEO smiled and said it was the first sign of a good market. He was concerned about the lack of competition up to that point.
Publish your book and let the market decide. Certainly don't let a pre-announcement of a book that's not fully written yet (yet alone reviewed) discourage you!
Yes, please do not forgo the completion of your book. I would love to hear about it once available as well. I have never had the chance to work in an environment where scaling PHP was necessary, and I am trying to gain all of the knowledge I possibly can on the subject so that I can take on bigger projects.
Dont get discouraged by this.
For example, Dropbox didnt get discouraged by the rumors of GDrive in 2007 and look where they are :) Of course totally different ball game, just saying: Try all you can before giving up especially since you are almost there!
The majority of readers of these books will not have products that require scaling to millions and will probably purchase both books. Sounds like market validation to me.
On the downside, I have a book cooking on the same exact subject, with release planned September (self-publish, about 80% done), but now not sure if it's worth continuing. [edit]Slight moment of "panic", as seeing someone else releasing a book on the same subject made me sad, but you're right, no reason not to continue.