ultrafast pdflatex with precompiling

Question

I try to improve the time pdflatex needs to compile my book.

Really working example

book.tex

%&preamble
\begin{document}
Hi
\end{document}

and

preamble.tex

\documentclass{article}

I run the following commands on bash console:

$ pdflatex -ini -jobname="preamble" "&pdflatex preamble.tex\dump"
$ latexmk -pdf -pvc -e '$latex=q/latex %O -shell-escape %S/' book.tex

A window opens with a (nearly) live preview that will be updated after each change in the book.tex file. The PDF Viewer evince reloads automatic when the .pdf changed.

Open Questions

I had no success to compile with the preamble of my book in the preamble.tex file.

• How can I find out what I can precompile?
• Can I precompile \newcommand's, \usepackage's?
• Can I precompile a pure chapter without header?

Other aproaches for speed up

(I do not understand how to combine this ideas for best result)

• pdflatex knows a -draftmode I measured 20% faster compilation with time pdflatex -draftmode 50pagetest.tex

Answer 1

"precompile" is probably a slightly confusing phrase to use as TeX is not a compiler but (mostly) a macro expansion language, but anyway...

In general you can dump most macro definitions and register assignments into a format. What you can't do is ship out pages. So in practice you can dump most LaTeX preambles.

Rather than having to edit the file so that it only works with the preloaded preamble format it is possible to leave the preamble as normal, but define the dumped format to skip the commands that were previously executed in the dump.

My truly ancient mylatex files on ctan do this or there is a newer version of that with additional features and better maintained: mylatexformat

The main thing you have to beware of (and which I suspect you are falling over) is if any of commands that you dump use \jobname (for example to open auxiliary files) then you have to ensure that the jobname when you dump the format is the same as the jobname when you produce the document. Also If the macros are assuming that files opened by commands in the preamble are still open when the document is processed then you will need to re-open them when you use your preloaded format loading the format file will re-set TeX's internal state with respect to its internal memory but it will not re-assign the file handles to the filesystem.

The first hit on searching for mylatex on this site shows an example discussing this in the context of tikz externalize.

TikZ's externalization and mylatex