214 lines
8.2 KiB
Markdown
214 lines
8.2 KiB
Markdown
[[!meta date="2009-10-15 18:42:46 -0400"]]
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Ikiwiki is a wiki compiler, which means that, unlike a traditional wiki,
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all the work needed to display your wiki is done up front. Where you can
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see it and get annoyed at it. In some ways, this is better than a wiki
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where a page view means running a program to generate the page on the fly.
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But enough excuses. If ikiwiki is taking too long to build your wiki,
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let's fix that. Read on for some common problems that can be avoided to
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make ikiwiki run quick.
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[[!toc]]
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(And if none of that helps, file a [[bug|bugs]]. One other great thing about
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ikiwiki being a wiki compiler is that it's easy to provide a test case when
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it's slow, and get the problem fixed!)
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## rebuild vs refresh
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Are you building your wiki by running a command like this?
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ikiwiki --setup my.setup
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If so, you're always telling ikiwiki to rebuild the entire site, from
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scratch. But, ikiwiki is smart, it can incrementally update a site,
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building only things affected by the changes you make. You just have to let
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it do so:
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ikiwiki --setup my.setup --refresh
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Ikiwiki automatically uses an incremental refresh like this when handing
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a web edit, or when run from a [[rcs]] post-commit hook. (If you've
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configured the hook in the usual way.) Most people who have run into this
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problem got in the habit of running `ikiwiki --setup my.setup` by hand
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when their wiki was small, and found it got slower as they added pages.
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## use the latest version
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If your version of ikiwiki is not [[!version]], try upgrading. New
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optimisations are frequently added to ikiwiki, some of them yielding
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*enormous* speed increases.
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## run ikiwiki in verbose mode
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Try changing a page, and run ikiwiki with `-v` so it will tell you
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everything it does to deal with that changed page. Take note of
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which other pages are rebuilt, and which parts of the build take a long
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time. This can help you zero in on individual pages that contain some of
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the expensive things listed below.
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## expensive inlines
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Do you have an archive page for your blog that shows all posts,
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using an inline that looks like this?
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\[[!inline pages="blog/*" show=0]]
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Or maybe you have some tag pages for your blog that show all tagged posts,
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something like this?
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\[[!inline pages="blog/* and tagged(foo)" show=0]]
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These are expensive, because they have to be updated whenever you modify a
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matching page. And, if there are a lot of pages, it generates a large html
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file, which is a lot of work. And also large RSS/Atom files, which is even
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more work!
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To optimise the inline, consider enabling quick archive mode. Then the
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inline will only need to be updated when new pages are added; no RSS
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or Atom feeds will be built, and the generated html file will be much
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smaller.
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\[[!inline pages="blog/*" show=0 archive=yes quick=yes]]
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\[[!inline pages="blog/* and link(tag)" show=0 archive=yes quick=yes]]
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Only downsides: This won't show titles set by the [[ikiwiki/directive/meta]]
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directive. And there's no RSS feed for users to use -- but if this page
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is only for the archives or tag for your blog, users should be subscribing
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to the blog's main page's RSS feed instead.
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For the main blog page, the inline should only show the latest N posts,
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which won't be a performance problem:
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\[[!inline pages="blog/*" show=30]]
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## expensive maps
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Do you have a sitemap type page, that uses a map directive like this?
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\[[!map pages="*" show=title]]
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This is expensive because it has to be updated whenever a page is modified.
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The resulting html file might get big and expensive to generate as you
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keep adding pages.
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First, consider removing the "show=title". Then the map will not show page
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titles set by the [[ikiwiki/directive/meta]] directive -- but will also
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only need to be generated when pages are added or removed, not for every
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page change.
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Consider limiting the map to only show the toplevel pages of your site,
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like this:
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\[[!map pages="* and !*/*" show=title]]
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Or, alternatively, to drop from the map parts of the site that accumulate
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lots of pages, like individual blog posts:
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\[[!map pages="* and !blog/*" show=title]]
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## sidebar issues
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If you enable the [[plugins/sidebar]] plugin, be careful of what you put in
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your sidebar. Any change that affects what is displayed by the sidebar
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will require an update of *every* page in the wiki, since all pages include
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the sidebar.
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Putting an expensive map or inline in the sidebar is the most common cause
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of problems. At its worst, it can result in any change to any page in the
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wiki requiring every page to be rebuilt.
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## avoid htmltidy
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A few plugins do neat stuff, but slowly. Such plugins are tagged
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[[plugins/type/slow]].
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The worst offender is possibly [[plugins/htmltidy]]. This runs an external
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`tidy` program on each page that is built, which is necessarily slow. So don't
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use it unless you really need it; consider using the faster
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[[plugins/htmlbalance]] instead.
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## be careful of large linkmaps
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[[plugins/Linkmap]] generates a cool map of links between pages, but
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it does it using the `graphviz` program. And any changes to links between
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pages on the map require an update. So, avoid using this to map a large number
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of pages with frequently changing links. For example, using it to map
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all the pages on a traditional, highly WikiLinked wiki, is asking for things
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to be slow. But using it to map a few related pages is probably fine.
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This site's own [[plugins/linkmap]] rarely slows it down, because it
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only shows the index page, and the small set of pages that link to it.
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That is accomplished as follows:
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\[[!linkmap pages="index or (backlink(index)"]]
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## overhead of the search plugin
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Be aware that the [[plugins/search]] plugin has to update the search index
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whenever any page is changed. This can slow things down somewhat.
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## cgi overload workaround
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If the ikiwiki.cgi takes a long time to run, it's possible
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that under load, your site will end up with many
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of them running, all waiting on some long-running thing,
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like a site rebuild. This can prevent the web server from doing anything
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else.
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A workaround for this problem is to set `cgi_overload_delay` to
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a number of seconds. Now if ikiwiki.cgi would block waiting
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for something, it will instead display a Please wait message (configurable
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via `cgi_overload_message`, which can contain arbitrary html),
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and set the page to reload it after the configured number of seconds.
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This takes very little load, as it all happens within compiled C code.
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Note that it is currently limited to GET requests, not POST requests.
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## scaling to large numbers of pages
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Finally, let's think about how huge number of pages can affect ikiwiki.
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* Every time it's run, ikiwiki has to scan your `srcdir` to find
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new and changed pages. This is similar in speed to running the `find`
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command. Obviously, more files will make it take longer.
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You can avoid this scanning overhead, if you're using git, by setting
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`only_committed_changes`. This makes ikiwiki --refresh query git for
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changed files since the last time, which tends to be a lot faster.
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However, it only works if all files in your wiki are committed to git
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(or stored in the [[/plugins/transient]] underlay).
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* Also, to see what pages match a [[ikiwiki/PageSpec]] like "blog/*", it has
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to check if every page in the wiki matches. These checks are done quite
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quickly, but still, lots more pages will make PageSpecs more expensive.
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* The backlinks calculation has to consider every link on every page
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in the wiki. (In practice, most pages only link to at most a few dozen
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other pages, so this is not a `O(N^2)`, but closer to `O(N)`.)
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* Ikiwiki also reads and writes an `index` file, which contains information
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about each page, and so if you have a lot of pages, this file gets large,
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and more time is spent on it. For a wiki with 2000 pages, this file
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will run about 500 kb.
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If your wiki will have 100 thousand files in it, you might start seeing
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the above contribute to ikiwiki running slowly.
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## profiling
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If you have a repeatable change that ikiwiki takes a long time to build,
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and none of the above help, the next thing to consider is profiling
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ikiwiki.
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The best way to do it is:
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* Install [[!cpan Devel::NYTProf]]
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* `PERL5OPT=-d:NYTProf`
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* `export PERL5OPT`
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* Now run ikiwiki as usual, and it will generate a `nytprof.out` file.
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* Run `nytprofhtml` to generate html files.
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* Those can be examined to see what parts of ikiwiki are being slow.
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