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| -rw-r--r-- | doc/bugs/Buggy_dependency_graph.mdwn | 44 |
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diff --git a/doc/bugs/Buggy_dependency_graph.mdwn b/doc/bugs/Buggy_dependency_graph.mdwn index 64e6695d2..116a2aea4 100644 --- a/doc/bugs/Buggy_dependency_graph.mdwn +++ b/doc/bugs/Buggy_dependency_graph.mdwn @@ -34,3 +34,47 @@ I observed these problems (same *kind*, I didn't check in details) on I can think about reducung the size of my wiki source and making it available online for analysis. -- NicolasLimare + +> As long as these dependencies don't grow over time (ie, when a page is +> edited and nothing changed that should add a dependency), I wouldn't +> worry about them. There are many things that can cause non-optimal +> dependencies to be recorded. For one thing, if you inline something, ikiwiki +> creates a dependency like: +> +> (PageSpec) or (file1 or file2 or file3 ...) +> +> Where fileN are all the files that the PageSpec currently matches. (This +> is ncessary to detect when a currently inlined file is deleted, and know +> the inlining page needs an update.) Now consider what it does if you have +> a single page with two inline statements, that inline the same set of +> stuff twice: +> +> ((PageSpec) or (file1 or file2 or file3 ...) or (PageSpec) or (file1 or file2 or file3 ...) +> +> Clearly non-optimal, indeed. +> +> Ikiwiki doesn't bother to simplify complex PageSpecs +> because it's difficult to do, and because all they use is some disk +> space. Consider what ikiwiki uses these dependencies for. +> All it wants to know is: does the PageSpec for this page it's considering +> rebuilding match any of the pages that have changed? Determining this is +> a simple operation -- the PageSpec is converted to perl code. The perl +> code is run. +> +> So the total impact of an ugly dependency like this is: +> +> 1. Some extra data read/written to disk. +> 2. Some extra space in memory. +> 3. A bit more data for the PageSpec translation code to handle. But that +> code is quite fast. +> 4. Typically one extra function call when the generated perl code is run. +> Ie, when the expression on the left-hand side fails, which typically +> happens after one (inexpensive) function call, it has to check +> the identical expression on the right hand side. +> +> So this is at best a wishlist todo item, not a bug. A PageSpec simplifier +> (or improved `pagespec_merge()` function) could be written and improve +> ikiwiki's memory and disk usage, but would it actually speed it up any? +> We'd have to see the code to the simplifier to know. +> +> --[[Joey]] |