Preloading TAGS and completion table (resend)

[Ludwig, Mark]

[Sorry, resending in plain text]

I use Emacs to maintain a large software system (>10,000,000 lines of code).  
We have multiple releases in the field under active maintenance (plus the next 
release under development).  I have cron jobs that make TAGS daily (overnight) 
because it takes hours to read the entire source in the multiple release source 
branches.  Each TAGS file per branch is over 40MB.  I run an instance of Emacs 
per release branch, because we use ClearCase, so the "same file name" 
potentially has different contents depending on the view (i.e., can't use Emacs 
Server across releases).

When I want to use tag completion, it takes about a minute for Emacs to 
construct the completion table.  Meanwhile, I can't do anything else in Emacs.  
I'm wondering if it's possible to get the completion table pre-loaded in the 
background, so when I am finding a tag and hit '?' I get an instantaneous 
response the first time, instead of a minute-long wait.

For context, I have been using EMACS/Emacs for over 30 years and my .emacs file 
is tiny, only pointing to another file with the real customization.  My 
customization is ~1,000 lines, and I byte-compile it.  I like pretending my 
name is Luke and using the source, but could use some tips and pointers about 
whether it's a good idea to try this in the background.  I'm not even sure it's 
possible to run this in the background (asynchronously).  Does Emacs have such 
asynchronous execution capability?

If asynchronous execution isn't possible or wise, I'll settle for a way to 
forcibly load the completion table (without my needing to manually trigger it). 
 I don't see a way to do that, either.

Thanks in advance!
Mark

P.S. If there is a better e-mail list for this question, please let me know.