The slowest part of a @racket[render] is parsing and decoding the source file. Often, previewing a single source file necessarily means decoding others (for instance templates, or other source files that are linked into the main source file). But usually, only one source file is changing at a time. Therefore, Pollen stores copies of the exports of source files —namely, whatever is stored in @code[(format "~a" world:main-export)] and @code[(format "~a" world:meta-export)] —in the cache so they can be reused.
The slowest part of a Pollen @racket[render] is compiling a source file. Because Pollen allows source files to be edited and previewed dynamically, these files get recompiled a lot. Therefore, Pollen stores copies of the exports of source files —namely, whatever is stored in @code[(format "~a" world:main-export)] and @code[(format "~a" world:meta-export)] —in a cache so they can be reused.
In each directory of your project, Pollen creates a subdirectory called @filepath{pollen-cache}. The files are stored on disk so they can be reused between sessions. If you delete files within a cache directory (or the whole thing), don't worry —everything will get regenerated. (However, you should not read or write to any @filepath{pollen-cache} directory, as the implementation details are subject to change.)
@section{Preloading and reseting}
Though the cache will be populated as you use Pollen, you can also preheat it with @exec{@seclink["raco_pollen_setup"]}. This command will load all your source files into the cache. This will give you the snappiest performance during an interactive session with the project server.
If you want to reset all the compile caches, use @exec{@seclink["raco_pollen_reset"]}.
@section{Disabling the cache}
The compile cache is controlled by the @seclink["settable-values"]{settable value} @racket[world:current-compile-cache-active]. Thus, to disable the compile cache, add a @racket[config] submodule to your @filepath{pollen.rkt} like so:
@codeblock|{
(module config racket/base
(provide (all-defined-out))
(define compile-cache-active #f))
}|
Pollen also caches rendered output files, so if you want to disable all caching —thus forcing everything to recompile, every time —you should also disable the render cache by setting @racket[world:current-render-cache-active]:
@codeblock|{
(module config racket/base
(provide (all-defined-out))
(define compile-cache-active #f)
(define render-cache-active #f))
}|
Be warned that this will make your rendering much slower. But you will be guaranteed an entirely fresh recompile each time, which can sometimes be useful in development.
@section{Scope of dependency tracking}
The compile cache tracks the modification date of the source file, the current setting of @secref["The_POLLEN_environment_variable"], and the modification dates of the template and @filepath{pollen.rkt} (if they exist).
It does not, however, track every possible dependency. So in a complex project, it's possible to create ``deep'' dependencies that aren't noticed by the cache.
Unfortunately, there's no way around this problem. For the cache to be useful, there has to be a limit on the horizon of dependency checking. For the cache to be totally certain that something hadn’t changed, it would have to compile afresh every time (which would be equivalent to not caching at all).
But those who need that kind of deep dynamism can disable the cache.
