SICStus Prolog

There are several things to do if the speed of the Emacs environment is a problem:

First of all, make sure that prolog.el and sicstus-support.el are compiled, i.e. that there is a prolog.elc and a sicstus-support.elc file at the same location as the original files. To do the compilation, start Emacs and type M-x byte-compile-file <RET> path <RET>, where path is the path to the *.el file. Do not be alarmed if there are a few warning messages as this is normal. If all went well, there should now be a compiled file, which is used the next time Emacs is started.
The next thing to try is changing the setting of prolog-use-prolog-tokenizer-flag to nil. This means that Emacs uses built-in functions for some of the source code parsing, thus speeding up indentation. The problem is that it does not handle all peculiarities of the Prolog syntax, so this is a trade-off between correctness and speed.
The setting of the prolog-parse-mode variable also affects the speed, 'beg-of-line being faster than 'beg-of-clause.
Font locking may be slow. You can turn it off using customization, available through M-x customize-group <RET> font-lock <RET>. An alternative is to enable one of the lazy font locking modes. You can also turn it off completely; see Basic Configuration.