v2writable: newest epochs go first in alternates

New epochs are the most likely to have loose objects.  git won't
be able to take advantage of pack indices and needs to scan
every alternate for the loose object via open/openat syscalls.
Those syscalls will add up some day when we've got hundreds or
thousands of epochs.

diff --git a/lib/PublicInbox/V2Writable.pm b/lib/PublicInbox/V2Writable.pm
index 9073d9ef89a8db95dd3db2d7c1b76cc26b758194..8ad71b54ee6fe7088a64e95637309ce914e9c790 100644 (file)
--- a/lib/PublicInbox/V2Writable.pm
+++ b/lib/PublicInbox/V2Writable.pm
@@ -663,23 +663,43 @@ sub fill_alternates ($$) {
        unless (-d $all) {
                PublicInbox::Import::init_bare($all);
        }
-       my $alt = "$all/objects/info/alternates";
-       my %alts;
-       my @add;
+       my $info_dir = "$all/objects/info";
+       my $alt = "$info_dir/alternates";
+       my (%alt, $new);
+       my $mode = 0644;
        if (-e $alt) {
                open(my $fh, '<', $alt) or die "open < $alt: $!\n";
-               %alts = map { chomp; $_ => 1 } (<$fh>);
+               $mode = (stat($fh))[2] & 07777;
+
+               # we assign a sort score to every alternate and favor
+               # the newest (highest numbered) one when we
+               my $score;
+               my $other = 0; # in case admin adds non-epoch repos
+               %alt = map {;
+                       if (m!\A\Q../../\E([0-9]+)\.git/objects\z!) {
+                               $score = $1 + 0;
+                       } else {
+                               $score = --$other;
+                       }
+                       $_ => $score;
+               } split(/\n+/, do { local $/; <$fh> });
        }
+
        foreach my $i (0..$epoch) {
                my $dir = "../../git/$i.git/objects";
-               push @add, $dir if !$alts{$dir} && -d "$pfx/$i.git";
-       }
-       return unless @add;
-       open my $fh, '>>', $alt or die "open >> $alt: $!\n";
-       foreach my $dir (@add) {
-               print $fh "$dir\n" or die "print >> $alt: $!\n";
+               if (!exists($alt{$dir}) && -d "$pfx/$i.git") {
+                       $alt{$dir} = $i;
+                       $new = 1;
+               }
        }
-       close $fh or die "close $alt: $!\n";
+       return unless $new;
+
+       my ($fh, $tmp) = tempfile('alt-XXXXXXXX', DIR => $info_dir);
+       print $fh join("\n", sort { $alt{$b} <=> $alt{$a} } keys %alt), "\n"
+               or die "print $tmp: $!\n";
+       chmod($mode, $fh) or die "fchmod $tmp: $!\n";
+       close $fh or die "close $tmp $!\n";
+       rename($tmp, $alt) or die "rename $tmp => $alt: $!\n";
 }
 
 sub git_init {

diff --git a/t/v2writable.t b/t/v2writable.t
index 63f27f962b896dd89653376f17e463b37311b312..7ceaa6e4c9cbda90a5787aff56445157bba1b95b 100644 (file)
--- a/t/v2writable.t
+++ b/t/v2writable.t
@@ -284,4 +284,28 @@ eval {
 };
 ok($@, 'V2Writable fails on non-existent dir');
 
+{
+       my $v2w = PublicInbox::V2Writable->new($tmp, 1);
+       ok($v2w, 'creat flag works');
+       $v2w->{parallel} = 0;
+       $v2w->init_inbox(0);
+       my $alt = "$tmp->{inboxdir}/all.git/objects/info/alternates";
+       open my $fh, '>>', $alt or die $!;
+       print $fh "$inboxdir/all.git/objects\n" or die $!;
+       chmod(0664, $fh) or die "fchmod: $!";
+       close $fh or die $!;
+       open $fh, '<', $alt or die $!;
+       my $before = do { local $/; <$fh> };
+
+       ok($v2w->git_init(3), 'init a new epoch');
+       open $fh, '<', $alt or die $!;
+       my $after = do { local $/; <$fh> };
+       ok(index($after, $before) > 0,
+               'old contents preserved after adding epoch');
+       like($after, qr!\A[^\n]+?/3\.git/objects\n!s,
+               'first line is newest epoch');
+       my $mode = (stat($alt))[2] & 07777;
+       is($mode, 0664, sprintf('0%03o', $mode).' is 0664');
+}
+
 done_testing();