ikiwiki/doc/todo/Improving_the_efficiency_of_match__95__glob.mdwn

[[!template id=gitbranch branch=smcv/ready/glob-cache
  author="[[KathrynAndersen]], [[smcv]]"]]
[[!tag patch]]

I've been profiling my IkiWiki to try to improve speed (with many pages makes speed even more important) and I've written a patch to improve the speed of match_glob.  This matcher is a good one to improve the speed of, because it gets called so many times.

Here's my patch - please consider it! -- [[KathrynAndersen]]

> It seems to me as though changing `glob2re` to return qr/$re/, and calling
> `memoize(glob2re)` next to the other memoize calls, would be a less
> verbose way to do this? --[[smcv]]

>> I think so, yeah. Anyway, do you have any benchmark results handy,
>> Kathryn?  --[[Joey]] 

>>> See below.
>>> Also, would it make more sense for glob2re to return qr/^$re$/i rather than qr/$re/?  Everything that uses glob2re seems to use
	$foo =~ /^$re$/i
>>> rather than /$re/ so I think that would make sense.
>>> -- [[KathrynAndersen]]

>>>> Git branch `smcv/ka-glob-cache` has Kathryn's patch. Git
>>>> branch `smcv/memoize-glob2re` does as I suggested, which
>>>> is less verbose than Kathryn's patch but also not as
>>>> fast; I'm not sure why, tbh. --[[smcv]]

>>>>> I think it's because my patch focuses on match_glob while the memoize patch focuses on `glob2re`, and `glob2re` is called in `filecheck`, `meta` and `po` as well as in `match_glob` and `match_user`; thus the memoized `glob2re` is dealing with a bigger set of globs to look up, and thus could be just that little bit slower. -- [[KathrynAndersen]]

>>>>>> What may be going on is that glob2re is already a fairly fast
>>>>>> function, so the overhead of memoizing it with the very generic
>>>>>> `_memoizer` (see its source) swamps the memoization gain. Note
>>>>>> that the few functions memoized with the Memoizer before were much
>>>>>> more expensive, so that little overhead was acceptable then.
>>>>>>
>>>>>> It also may be that Kathryn's patch is slightly faster due to using
>>>>>> the construct `$foo =~ $regexp` rather than `$foo =~ /$regexp/`
>>>>>> (probably avoids a copy or something like that internally) --
>>>>>> this despite checking both `exists` and `defined` on the hash, which
>>>>>> should be reundant AFAICS.
>>>>>>
>>>>>> My guess is that the best of both worlds would be to move
>>>>>> the byhand memoization to glob2re and have it return a compiled
>>>>>> `/^/i` regexp that can be used without further modifiction in most
>>>>>> cases. --[[Joey]] 

>>>>>>> Done, see `smcv/ready/glob-cache` and `smcv/glob-cache-too-far`.
>>>>>>>
>>>>>>> Kathryn's patch is a significant improvement; my first patch on top of
>>>>>>> that is a trivial cleanup that speeds it up a little, and the next two
>>>>>>> patches (using precompiled regexes) have surprisingly little effect
>>>>>>> (they don't slow it down either though, so either omit them or merge
>>>>>>> them, whichever). Detailed benchmark results below.
>>>>>>>
>>>>>>> Moving the memoization to `glob2re` actually seems to slow things down
>>>>>>> again - I suspect the docwiki has few enough mentions of `user()` etc.
>>>>>>> that caching them is a waste of time, but perhaps it's not the most
>>>>>>> representative.
>>>>>>> --[[smcv]]

[[done]] --[[Joey]] 

--------------------------------------------------------------

[[!toggle id="smcv-benchmark" text="current benchmarks"]]

[[!toggleable id="smcv-benchmark" text="""
master at time of branch:

    time elapsed (wall):   29.6348
    time running program:  24.9212  (84.09%)
    time profiling (est.): 4.7136  (15.91%)
    number of calls:       1360181
    number of exceptions:  13
    
    %Time    Sec.     #calls   sec/call  F  name
    13.24    3.2986     3408   0.000968     Text::Balanced::_match_tagged
    10.94    2.7253    79514   0.000034     IkiWiki::PageSpec::match_glob
     3.19    0.7952    59454   0.000013     <anon>:IkiWiki/Plugin/inline.pm:223

`Improve the speed of match_glob`:

    time elapsed (wall):   27.9755
    time running program:  23.5293  (84.11%)
    time profiling (est.): 4.4461  (15.89%)
    number of calls:       1280875
    number of exceptions:  13
    
    %Time    Sec.     #calls   sec/call  F  name
    14.56    3.4257     3408   0.001005     Text::Balanced::_match_tagged
     7.82    1.8403    79514   0.000023     IkiWiki::PageSpec::match_glob
     3.27    0.7698    59454   0.000013     <anon>:IkiWiki/Plugin/inline.pm:223

`match_glob: streamline glob cache slightly`:

    time elapsed (wall):   27.5753
    time running program:  23.1714  (84.03%)
    time profiling (est.): 4.4039  (15.97%)
    number of calls:       1280875
    number of exceptions:  13
    
    %Time    Sec.     #calls   sec/call  F  name
    14.09    3.2637     3408   0.000958     Text::Balanced::_match_tagged
     7.74    1.7926    79514   0.000023     IkiWiki::PageSpec::match_glob
     3.30    0.7646    59454   0.000013     <anon>:IkiWiki/Plugin/inline.pm:223

`glob2re: return a precompiled, anchored case-insensitiv...`:

    time elapsed (wall):   27.5656
    time running program:  23.1464  (83.97%)
    time profiling (est.): 4.4192  (16.03%)
    number of calls:       1282189
    number of exceptions:  13
    
    %Time    Sec.     #calls   sec/call  F  name
    14.21    3.2891     3408   0.000965     Text::Balanced::_match_tagged
     7.72    1.7872    79514   0.000022     IkiWiki::PageSpec::match_glob
     3.32    0.7678    59454   0.000013     <anon>:IkiWiki/Plugin/inline.pm:223

`make use of precompiled regex objects`:

    time elapsed (wall):   27.5357
    time running program:  23.1289  (84.00%)
    time profiling (est.): 4.4068  (16.00%)
    number of calls:       1281981
    number of exceptions:  13
    
    %Time    Sec.     #calls   sec/call  F  name
    14.17    3.2776     3408   0.000962     Text::Balanced::_match_tagged
     7.70    1.7814    79514   0.000022     IkiWiki::PageSpec::match_glob
     3.35    0.7756    59454   0.000013     <anon>:IkiWiki/Plugin/inline.pm:223

`move memoization from match_glob to glob2re`:

    time elapsed (wall):   28.7677
    time running program:  23.9473  (83.24%)
    time profiling (est.): 4.8205  (16.76%)
    number of calls:       1360181
    number of exceptions:  13
    
    %Time    Sec.     #calls   sec/call  F  name
    13.98    3.3469     3408   0.000982     Text::Balanced::_match_tagged
     8.85    2.1194    79514   0.000027     IkiWiki::PageSpec::match_glob
     3.24    0.7750    59454   0.000013     <anon>:IkiWiki/Plugin/inline.pm:223

--[[smcv]]
"""]]

--------------------------------------------------------------

[[!toggle id="ka-benchmarks" text="Kathryn's benchmarks"]]

[[!toggleable id="ka-benchmarks" text="""
Benchmarks done with Devel::Profile on the same testbed IkiWiki setup.  I'm just showing the start of the profile output, since that's what's relevant.

Before:
<pre>
time elapsed (wall):   27.4173
time running program:  22.5909  (82.40%)
time profiling (est.): 4.8264  (17.60%)
number of calls:       1314729
number of exceptions:  65

%Time    Sec.     #calls   sec/call  F  name
11.05    2.4969    62333   0.000040     IkiWiki::PageSpec::match_glob
 4.10    0.9261      679   0.001364     Text::Balanced::_match_tagged
 2.72    0.6139    59812   0.000010     IkiWiki::SuccessReason::merge_influences
</pre>

After:
<pre>
time elapsed (wall):   26.1843
time running program:  21.5673  (82.37%)
time profiling (est.): 4.6170  (17.63%)
number of calls:       1252433
number of exceptions:  65

%Time    Sec.     #calls   sec/call  F  name
 7.66    1.6521    62333   0.000027     IkiWiki::PageSpec::match_glob
 4.33    0.9336      679   0.001375     Text::Balanced::_match_tagged
 2.81    0.6057    59812   0.000010     IkiWiki::SuccessReason::merge_influences
</pre>

Note that the seconds per call for match_glob in the "after" case has gone down by about a third.

K.A.
"""]]

--------------------------------------------------------------

[[!toggle id="ka-patch" text="Kathryn's original patch"]]

[[!toggleable id="ka-patch" text="""

<pre>
diff --git a/IkiWiki.pm b/IkiWiki.pm
index 08a3d78..c187b98 100644
--- a/IkiWiki.pm
+++ b/IkiWiki.pm
@@ -2482,6 +2482,8 @@ sub derel ($$) {
 	return $path;
 }
 
+my %glob_cache;
+
 sub match_glob ($$;@) {
 	my $page=shift;
 	my $glob=shift;
@@ -2489,8 +2491,15 @@ sub match_glob ($$;@) {
 	
 	$glob=derel($glob, $params{location});
 
-	my $regexp=IkiWiki::glob2re($glob);
-	if ($page=~/^$regexp$/i) {
+	# Instead of converting the glob to a regex every time,
+	# cache the compiled regex to save time.
+	if (!exists $glob_cache{$glob}
+	    or !defined $glob_cache{$glob})
+	{
+	    my $re=IkiWiki::glob2re($glob);
+	    $glob_cache{$glob} = qr/^$re$/i;
+	}
+	if ($page =~ $glob_cache{$glob}) {
 		if (! IkiWiki::isinternal($page) || $params{internal}) {
 			return IkiWiki::SuccessReason->new("$glob matches $page");
 		}
</pre>
"""]]
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