(no commit message)

[git.ikiwiki.info.git] / doc / todo / headless_git_branches.mdwn

diff --git a/doc/todo/headless_git_branches.mdwn b/doc/todo/headless_git_branches.mdwn
index 280405730f27bc4be1cba0fded7b511c84aceec6..d9bb38099d052c57417f9c4b9c5e69114405a26b 100644 (file)
--- a/doc/todo/headless_git_branches.mdwn
+++ b/doc/todo/headless_git_branches.mdwn
@@ -6,7 +6,9 @@ Ikiwiki should really survive being asked to work with a git branch that has no
     git clone barerepo.git srcdir
     ikiwiki --rcs=git srcdir destdir
 
     git clone barerepo.git srcdir
     ikiwiki --rcs=git srcdir destdir
 

-I've fixed this initial construction case, and, based on my testing, I've also fixed the post-update executing on a new master, and ikiwiki.cgi executing on a non-existent master cases.
+I've fixed this initial construction case, and, based on my testing, I've
+also fixed the post-update executing on a new master, and ikiwiki.cgi
+executing on a non-existent master cases.

 
 Please commit so my users stop whining at me about having clean branches to push to, the big babies.
 
 
 Please commit so my users stop whining at me about having clean branches to push to, the big babies.
 


@@ -14,30 +16,38 @@ Summary: Change three scary loud failure cases related to empty branches into th
 
 [[!tag patch]]
 
 
 [[!tag patch]]
 

+> FWIW, [[The_TOVA_Company]] apparently wants this feature (and I hope
+> I don't mind that I mention they were willing to pay someone for it,
+> but I told them I'd not done any of the work. :) )
+> 
+> Code review follows, per hunk.. --[[Joey]] 
+

 <pre>
 diff --git a/IkiWiki/Plugin/git.pm b/IkiWiki/Plugin/git.pm
 <pre>
 diff --git a/IkiWiki/Plugin/git.pm b/IkiWiki/Plugin/git.pm

-index cf7fbe9..a1b5ed3 100644
+index cf7fbe9..e5bafcf 100644

 --- a/IkiWiki/Plugin/git.pm
 +++ b/IkiWiki/Plugin/git.pm
 --- a/IkiWiki/Plugin/git.pm
 +++ b/IkiWiki/Plugin/git.pm

-@@ -439,17 +439,20 @@ sub git_commit_info ($;$) {
+@@ -439,17 +439,21 @@ sub git_commit_info ($;$) {

  
        my @opts;
        push @opts, "--max-count=$num" if defined $num;
  
        my @opts;
        push @opts, "--max-count=$num" if defined $num;

-+      my @raw_lines;
-+      my @ci;
- 
+-

 -      my @raw_lines = run_or_die('git', 'log', @opts,
 -              '--pretty=raw', '--raw', '--abbrev=40', '--always', '-c',
 -              '-r', $sha1, '--', '.');
 -      my @raw_lines = run_or_die('git', 'log', @opts,
 -              '--pretty=raw', '--raw', '--abbrev=40', '--always', '-c',
 -              '-r', $sha1, '--', '.');

-+      if (-e $config{srcdir} . '/.git/refs/heads/' . $config{gitmaster_branch}) {
-+              @raw_lines = run_or_die('git', 'log', @opts,
-+                      '--pretty=raw', '--raw', '--abbrev=40', '--always', '-c',
-+                      '-r', $sha1, '--', '.');
- 
--      my @ci;
+-
++      my @raw_lines;
+       my @ci;

 -      while (my $parsed = parse_diff_tree(\@raw_lines)) {
 -              push @ci, $parsed;
 -      }
 -      while (my $parsed = parse_diff_tree(\@raw_lines)) {
 -              push @ci, $parsed;
 -      }

++        
++      # Test to see if branch actually exists yet.
++      if (run_or_non('git', 'show-ref', '--quiet', '--verify', '--', 'refs/heads/' . $config{gitmaster_branch}) ) {
++              @raw_lines = run_or_die('git', 'log', @opts,
++                      '--pretty=raw', '--raw', '--abbrev=40', '--always', '-c',
++                      '-r', $sha1, '--', '.');
++

 +              while (my $parsed = parse_diff_tree(\@raw_lines)) {
 +                      push @ci, $parsed;
 +              }
 +              while (my $parsed = parse_diff_tree(\@raw_lines)) {
 +                      push @ci, $parsed;
 +              }


@@ -48,19 +58,110 @@ index cf7fbe9..a1b5ed3 100644
  
        return wantarray ? @ci : $ci[0];
  }
  
        return wantarray ? @ci : $ci[0];
  }

-@@ -474,7 +477,10 @@ sub rcs_update () {
+</pre>
+
+My concern is that this adds a bit of slowdown (git show-ref is fast, but
+It's still extra work) to a very hot code path that is run to eg,
+update recentchanges after every change. 
+
+Seems not ideal to do extra work every time to handle a case
+that will literally happen a maximum of once in the entire lifecycle of a
+wiki (and zero times more typically, since the setup automator puts in a
+.gitignore file that works around this problem).
+
+So as to not just say "no" ... what if it always tried to run git log,
+and if it failed (or returned no parsed lines), then it could look 
+at git show-ref to deduce whether to throw an error or not.
+--[[Joey]] 
+
+> Ah, but then git-log would still complain "bad revision 'HEAD'"
+> --[[Joey]] 
+
+    jrayhawk@piny:/srv/git/jrayhawk.git$ time perl -e 'for( $i = 1; $i < 10000; $i++) { system("git", "show-ref", "--quiet", "--verify", "--", "refs/heads/master"); }'
+    
+    real  0m10.988s
+    user  0m0.120s
+    sys   0m1.210s
+
+> FWIW, "an extra millisecond per edit" vs "full git coverage" is no
+> contest for me; I use that patch on seven different systems, including
+> freedesktop.org, because I've spent more time explaining to users either
+> why Ikiwiki won't work on their empty repositories or why their
+> repositories need useless initial commits (a la Branchable) that make
+> pushing not work and why denyNonFastForwards=0 and git push -f are
+> necessary than all the milliseconds that could've been saved in the
+> world.
+> 
+> But, since we're having fun rearranging deck chairs on the RMS Perl
+> (toot toot)...
+> 
+> There's some discrepency here I wasn't expecting:
+
+    jrayhawk@piny:/srv/git/jrayhawk.git$ time dash -c 'i=0; while [ $i -lt 10000 ]; do i=$((i+1)); git show-ref --quiet --verify -- refs/heads/master; done'
+    
+    real  0m9.986s
+    user  0m0.170s
+    sys   0m0.940s
+
+> While looking around in the straces, I notice Perl, unlike {b,d}ash
+> appears to do PATH lookup on every invocation of git, adding up to
+> around 110 microseconds apiece on a post-2.6.38 16-thread QPI system:
+
+    29699      0.000112 execve("/home/jrayhawk/bin/git", ["git", "show-ref", "--quiet", "--verify", "--", "refs/heads/master"], [/* 17 vars */]) = -1 ENOENT (No such file or directory)
+    29699      0.000116 execve("/usr/local/bin/git", ["git", "show-ref", "--quiet", "--verify", "--", "refs/heads/master"], [/* 17 vars */]) = -1 ENOENT (No such file or directory)
+    29699      0.000084 execve("/usr/bin/git", ["git", "show-ref", "--quiet", "--verify", "--", "refs/heads/master"], [/* 17 vars */]) = 0
+
+> You can probably save a reasonable number of context switches and
+> RCU-heavy (or, previously, lock-heavy) dentry lookups by doing a Perl
+> equivalent of `which git` and using the result. It might even add up to
+> a whole millisecond in some circumstances!
+> 
+> No idea where the rest of that time is going. Probably cache misses
+> on the giant Perl runtime or something.
+> 
+> ...
+> 
+> Now I feel dirty for having spent more time talking about optimization
+> than that optimization is likely to save. This must be what being an
+> engineer feels like.
+> --jrayhawk
+
+<pre>
+@@ -474,7 +478,10 @@ sub rcs_update () {

        # Update working directory.
  
        if (length $config{gitorigin_branch}) {
 -              run_or_cry('git', 'pull', '--prune', $config{gitorigin_branch});
 +              run_or_cry('git', 'fetch', '--prune', $config{gitorigin_branch});
        # Update working directory.
  
        if (length $config{gitorigin_branch}) {
 -              run_or_cry('git', 'pull', '--prune', $config{gitorigin_branch});
 +              run_or_cry('git', 'fetch', '--prune', $config{gitorigin_branch});

-+              if (-e $config{srcdir} . '/.git/refs/remotes/' . $config{gitorigin_branch} . '/' . $config{gitmaster_branch}) {
++              if (run_or_non('git', 'show-ref', '--quiet', '--verify', '--', 'refs/remotes/' . $config{gitorigin_branch} . '/' . $config{gitmaster_branch}) ) {

 +                      run_or_cry('git', 'merge', $config{gitorigin_branch} . '/' . $config{gitmaster_branch});
 +              }
        }
  }
 +                      run_or_cry('git', 'merge', $config{gitorigin_branch} . '/' . $config{gitmaster_branch});
 +              }
        }
  }

- 
-@@ -559,7 +565,7 @@ sub rcs_commit_helper (@) {
+
+</pre>
+
+Same concern here about extra work. Code path is nearly as hot, being
+called on every refresh. Probably could be dealt with similarly as above.
+
+Also, is there any point in breaking the pull up into a
+fetch followed by a merge? --[[Joey]] 
+
+> The same benchmarking applies, at least.
+>
+> Re: fetch/merge: We can't test for the nonexistence of the origin branch
+> without fetching it, and we can't merge it if it is, indeed,
+> nonexistant.
+>
+> Unless you're implying that it would be better to just spam stderr with
+> unnecessary scary messages and/or ignore/suppress them and lose the
+> ability to respond appropriately to every other error condition. As
+> maintainer, you deal with a disproportionate amount of the resulting
+> support fallout, so I'm perfectly satisfied letting you make that call.
+> --jrayhawk
+
+<pre>
+@@ -559,7 +566,7 @@ sub rcs_commit_helper (@) {

        # So we should ignore its exit status (hence run_or_non).
        if (run_or_non('git', 'commit', '-m', $params{message}, '-q', @opts)) {
                if (length $config{gitorigin_branch}) {
        # So we should ignore its exit status (hence run_or_non).
        if (run_or_non('git', 'commit', '-m', $params{message}, '-q', @opts)) {
                if (length $config{gitorigin_branch}) {


@@ -70,3 +171,8 @@ index cf7fbe9..a1b5ed3 100644
        }
        
 </pre>
        }
        
 </pre>

+
+This seems fine to apply. --[[Joey]]
+
+> Hooray!
+> --jrayhawk