+## PROFILING slow render : Case buggy [[plugins/filecheck]] ?
+
+Saving an article from ikiwiki editor is long ?
+<tt>ikiwiki --setup wiki.setup --rebuild</tt> is long ?
+
+Of course it depends the size of the wiki but if it's tiny and still take
+more that two minutes, it's boring. But if it takes a **dozen of minutes**, it's plain buggy.
+
+Actually one can with a verbose rebuild narrow down which page "lags" :
+
+<code>
+ private/admin.mdmn
+ tag/admin
+ tag/private
+</code>
+
+It's also possible to measure render time on one of these pages like this:
+
+<code>
+time ikiwiki --setup wiki.setup --render private/admin.mdwn
+</code>
+
+Well indeed for such a simple page, something fishy is going on.
+
+Still for simple yet superficial but enough profiling test, it requires
+a sub-level perl profiler.
+
+## Using SmallProf
+
+[[tips/optimising_ikiwiki/#index10h2]] proposed [[!cpan Devel::NYTProf]].
+
+Try it hard to make it spits realistic numbers or even a trend to point
+the bottleneck in the code. Bref -- nothing valuable nor coherent, it's way to sophisticated to be handy
+in my situation (virtual machine, SMP system, long runs, clock drifts, etc...)
+
+[[!cpan Devel::SmallProf]] is simple and just works(c)
+
+<pre>
+export PERL5OPT=-d:SmallProf
+time ikiwiki --setup wiki.setup --rebuild
+sort -k 2nr,2 -k 3nr,3 smallprof.out | head -n 6
+</pre>
+
+
+### Results : 6 top slowpits
+
+Total rebuild time:<br/>
+real 5m16.283s<br/>
+user 2m38.935s<br/>
+sys 2m32.704s<br/>
+
+
+Total rebuild time (under profiling) : <br/>
+real 19m21.633s<br/>
+user 14m47.831s<br/>
+sys 4m11.046s<br/>
+
+
+<pre>
+[num] [walltime] [cputime] [line]: [code]
+3055 114.17165 15.34000 149: $mimetype=<$file_h>;
+1626527 69.39272 101.4700 93: read($fh, $line, $$ref[1]); # read max
+3055 50.62106 34.78000 148: open(my $file_h, "-|", "file", "-bi",
+1626527 14.86525 48.50000 92: seek($fh, $$ref[0], SEEK_SET); # seek
+1626527 13.95613 44.78000 102: return undef unless $line =~ $$ref[3]; #
+3055 5.75528 5.81000 76: for my $type (map @$_, @rules) {
+</pre>
+
+legend :
+*num* is the number of times that the line was executed, *time* is the amount of "wall time" (time according the the clock on the wall vs. cpu time)
+spent executing it, *ctime* is the amount of cpu time expended on it and *line* and *code* are the line number and the actual text of the executed line
+(read from the file).
+
+
+3 topmost issues are located in this file :
+
+<tt>/usr/lib/perl5/vendor_perl/5.12.3/IkiWiki/Plugin/filecheck.pm</tt>
+<pre>
+sub match_mimetype ($$;@) {
+ my $page=shift;
+ my $wanted=shift;
+
+ my %params=@_;
+ my $file=exists $params{file} ? $params{file} : IkiWiki::srcfile($IkiWiki::pagesources{$page});
+ if (! defined $file) {
+ return IkiWiki::ErrorReason->new("file does not exist");
+ }
+
+ # Get the mime type.
+ #
+ # First, try File::Mimeinfo. This is fast, but doesn't recognise
+ # all files.
+ eval q{use File::MimeInfo::Magic};
+ my $mimeinfo_ok=! $@;
+ my $mimetype;
+ if ($mimeinfo_ok) {
+ my $mimetype=File::MimeInfo::Magic::magic($file);
+ }
+
+ # Fall back to using file, which has a more complete
+ # magic database.
+ if (! defined $mimetype) {
+ open(my $file_h, "-|", "file", "-bi", $file);
+ $mimetype=<$file_h>;
+ chomp $mimetype;
+ close $file_h;
+ }
+ if (! defined $mimetype || $mimetype !~s /;.*//) {
+ # Fall back to default value.
+ $mimetype=File::MimeInfo::Magic::default($file)
+ if $mimeinfo_ok;
+ if (! defined $mimetype) {
+ $mimetype="unknown";
+ }
+ }
+
+ my $regexp=IkiWiki::glob2re($wanted);
+ if ($mimetype!~$regexp) {
+ return IkiWiki::FailReason->new("file MIME type is $mimetype, not $wanted");
+ }
+ else {
+ return IkiWiki::SuccessReason->new("file MIME type is $mimetype");
+ }
+}
+</pre>
+
+Next 3 in this file :
+
+<tt>/usr/lib/perl5/vendor_perl/5.12.3/File/MimeInfo/Magic.pm</tt>
+<pre>
+sub _check_rule {
+ my ($ref, $fh, $lev) = @_;
+ my $line;
+
+ # Read
+ if (ref $fh eq 'GLOB') {
+ seek($fh, $$ref[0], SEEK_SET); # seek offset
+ read($fh, $line, $$ref[1]); # read max length
+ }
+ else { # allowing for IO::Something
+ $fh->seek($$ref[0], SEEK_SET); # seek offset
+ $fh->read($line, $$ref[1]); # read max length
+ }
+
+ # Match regex
+ $line = unpack 'b*', $line if $$ref[2]; # unpack to bits if using mask
+ return undef unless $line =~ $$ref[3]; # match regex
+ print STDERR '>', '>'x$lev, ' Value "', _escape_bytes($2),
+ '" at offset ', $$ref[1]+length($1),
+ " matches at $$ref[4]\n"
+ if $DEBUG;
+ return 1 unless $#$ref > 4;
+
+ # Check nested rules and recurs
+ for (5..$#$ref) {
+ return 1 if _check_rule($$ref[$_], $fh, $lev+1);
+ }
+ print STDERR "> Failed nested rules\n" if $DEBUG && ! $lev;
+ return 0;
+}
+</pre>
+
+*"It seems it's a unique cause, that snails it all"*
+
+## Conclusion
+
+This describes an issue in the attachment filechecker with mime type detection.
+The smallprof out file reveals it always fall back to using file which is very time-consuming.
+
+So what the hell did I put as complex allowed file attachment ruining File::Mimeinfo fast yet sparse recon ?
+Well, it was set in the config this way:
+
+<tt>allowed_attachments => 'mimetype(image/*) or maxsize(5000kb) or mimetype(text/plain) or mimetype(text/css) or mimetype(video/*)'</tt>
+
+Ok... maybe the wildcards induce ....hum whatever... let's try something , the simplest thing :
+
+<tt>allowed_attachments => 'mimetype(text/plain) or mimetype(text/css)'</tt>
+
+Same slowness : yek, File::Mimeinfo recons nothing ... not even simplest files.
+
+Disabling it is a temporary cure obviously but it only took **30 seconds** .
+
+<tt>disable_plugins => [qw{filecheck}]</tt>
+
+I tried also to upgrade [[!cpan File::MimeInfo]] to current 0.16, did not helped either. :/
+
+I opened a bug [[bugs/Slow_Filecheck_attachments___34__snails_it_all__34__]]
+