ikiwiki/doc/todo/optimize_simple_dependencies.mdwn

I'm still trying to optimize ikiwiki for a site using
[[plugins/contrib/album]], and checking which pages depend on which pages
is still taking too long. Here's another go at fixing that, using [[Will]]'s
suggestion from [[todo/should_optimise_pagespecs]]:

> A hash, by itself, is not optimal because
> the dependency list holds two things: page names and page specs.  The hash would
> work well for the page names, but you'll still need to iterate through the page specs.
> I was thinking of keeping a list and a hash.  You use the list for pagespecs
> and the hash for individual page names.  To make this work you need to adjust the
> API so it knows which you're adding.  -- [[Will]]

If you have P pages and refresh after changing C of them, where an average
page has E dependencies on exact page names and D other dependencies, this
branch should drop the complexity of checking dependencies from
O(P * (D+E) * C) to O(C + P*E + P*D*C). Pages that use inline or map have
a large value for E (e.g. one per inlined page) and a small value for D (e.g.
one per inline).

Benchmarking:

Test 1: a wiki with about 3500 pages and 3500 photos, and a change that
touches about 350 pages and 350 photos

Test 2: the docwiki (about 700 objects not excluded by docwiki.setup, mostly
pages), docwiki.setup modified to turn off verbose, and a change that touches
the 98 pages of plugins/*.mdwn

In both tests I rebuilt the wiki with the target ikiwiki version, then touched
the appropriate pages and refreshed.

Results of test 1: without this branch it took around 5:45 to rebuild and
around 5:45 again to refresh (so rebuilding 10% of the pages, then deciding
that most of the remaining 90% didn't need to change, took about as long as
rebuilding everything). With this branch it took 5:47 to rebuild and 1:16
to refresh.

Results of test 2: rebuilding took 14.11s without, 13.96s with; refreshing
three times took 7.29/7.40/7.37s without, 6.62/6.56/6.63s with.

(This benchmarking was actually done with my [[plugins/contrib/album]] branch,
since that's what the huge wiki needs; that branch doesn't alter core code
beyond the ready/depends-exact branch point, so the results should be
equally valid.)

--[[smcv]]

> Now [[merged|done]] --[[smcv]]

----

> We discussed this on irc; I had some worries that things may have been
> switched to `add_depends_exact` that were not pure page names. My current
> feeling is it's all safe, but who knows. It's easy to miss something.
> Which makes me think this is not a good interface.
> 
> Why not, instead, make `add_depends` smart. If it's passed something
> that is clearly a raw page name, it can add it to the exact depends hash.
> Else, add it to the pagespec hash. You can tell if it's a pure page name
> by matching on `$config{wiki_file_regexp}`.

>> Good thinking. Done in commit 68ce514a 'Auto-detect "simple dependencies"',
>> with a related bugfix in e8b43825 "Force %depends_exact to lower case".
>>
>> Performance impact: Test 2 above takes 0.2s longer to rebuild (probably
>> from all the calls to lc, which are, however, necessary for correctness)
>> and has indistinguishable performance for a refresh.
>>
>> Test 1 took about 6 minutes to rebuild and 1:25 to refresh; those are
>> pessimistic figures, since I've added 90 more photos and 90 more pages
>> (both to the wiki as a whole, and the number touched before refreshing)
>> since testing the previous version of this branch. --[[smcv]]

> Also I think there may be little optimisation value left in
> 7227c2debfeef94b35f7d81f42900aa01820caa3, since the "regular" dependency
> lists will be much shorter.

>> You're probably right, but IMO it's not worth reverting it - a set (hash with
>> dummy values) is still the right data structure. --[[smcv]]

> Sounds like inline pagenames has an already exstant bug WRT
> pages moving, which this should not make worse. Would be good to verify.

>> If you mean the standard "add a better match for a link-like construct" bug
>> that also affects sidebar, then yes, it does have the bug, but I'm pretty
>> sure this branch doesn't make it any worse. I could solve this at the cost
>> of making pagenames less useful for interactive use, by making it not
>> respect [[ikiwiki/subpage/LinkingRules]], but instead always interpret
>> its paths as relative to the top of the wiki - that's actually all that
>> [[plugins/contrib/album]] needs. --[[smcv]]

> Re coding, it would be nice if `refresh()` could avoid duplicating
> the debug message, etc in the two cases. --[[Joey]]

>> Fixed in commit f805d566 "Avoid duplicating debug message..." --[[smcv]]