I don't know the techniques they use, however, I may be able to shed some light from a general systems viewpoint:

First and formost, pdflatex is a CPU-bound program (see Tips for choosing hardware for best LaTeX compile performance). On any modern operating system and hardware it should take less than a couple of milliseconds to start it inside a new process and this startup time should be insignificant in relation to the computational work done for the typesetting. Hence, even in a massive multi-user setting, the benefits of running it inside a preloaded daemon would be relatively small. 

Most disk IO is related to a restricted set of files (the standard classes and packages), which therefore will reside in the buffer cache. However, on a standard server today, it would even be not a problem to cache all TexLive packages and fonts (hey, this are just a few GiB). 

If hundreds or thousands of program instances run in parallel, their memory working sets would furthermore share large parts of the physical memory. Basically, all non-volatile memory (program code, constant data) is shared among all pdflatex processes. Under the hood, the operating system initially "shares everything" and transparently creates a private copy of each memory page only when a process attempts to write to it. So memory that is never written remains always shared.

To sum up: Given a modern hardware and operating-system environment, I would not expect signficant benefits by the daemon approach.  

Do the online LaTeX compilers use a TeX daemon to speed up their compilation?
I am a programmer and I Google a lot.

The problem.

The thing is that it seems that Google finds my search requests fishy (often related to security and compile errors, something casual users won't search for) and asks me to enter captchas from time to time.

It all started something about a year ago - I've found myself entering captchas a couple of times a week - not really pleasant, but something one can live with. Sometime about half a year ago the situation got worse - Google asked me to enter captchas up to 5 times a day (!), but after some time it eased a bit and lately I've been entering captchas about once a week. Last week Google started to ask me double captchas (asks one and another immediately. First captcha was entered 100% correct - I triple checked it).

It is true that I sometimes search really weird stuff but captchas keep being asked even for casual queries. Also it happens when I Google on different OSes (Windows/Ubuntu) and in different browsers (Firefox/Chrome), so I suspect that this is something that is relevant to my google profile.

What I tried.


Dug through Google account preferences - found nothing useful.
Saw some articles and tutorials on the internet (like this for example), but all that I stumbled upon was outdated and didn't help me to solve my problem.




So, in the end, what can I do to confirm that I am a human once and for all, or at least reduce amount of captchas that I have to enter while Googling?
