xcpdb: avoid race when shards are added

[public-inbox.git] / lib / PublicInbox / Xapcmd.pm

diff --git a/lib/PublicInbox/Xapcmd.pm b/lib/PublicInbox/Xapcmd.pm
index daef896c37e9a435639505211d7d68e3f74a531f..44e0f8e58dca6ac1374ce01d953252a9f7a4bb8c 100644 (file)
--- a/lib/PublicInbox/Xapcmd.pm
+++ b/lib/PublicInbox/Xapcmd.pm
@@ -20,16 +20,23 @@ sub commit_changes ($$$$) {
        my $reshard = $opt->{reshard};
 
        $SIG{INT} or die 'BUG: $SIG{INT} not handled';
-       my @old_shard;
-       my $over_chg;
-       my $mode;
-
-       while (my ($old, $newdir) = each %$tmp) {
+       my (@old_shard, $over_chg);
+
+       # Sort shards highest-to-lowest, since ->xdb_shards_flat
+       # determines the number of shards to load based on the max;
+       # and we'd rather xdb_shards_flat to momentarily fail rather
+       # than load out-of-date shards
+       my @order = sort {
+               my ($x) = ($a =~ m!/([0-9]+)/*\z!);
+               my ($y) = ($b =~ m!/([0-9]+)/*\z!);
+               ($y // -1) <=> ($x // -1) # we may have non-shards
+       } keys %$tmp;
+
+       my ($dname) = ($order[0] =~ m!(.*/)[^/]+/*\z!);
+       my $mode = (stat($dname))[2];
+       for my $old (@order) {
                next if $old eq ''; # no invalid paths
-               $mode //= do {
-                       my ($dname) = ($old =~ m!(.*/)[^/]+/*\z!);
-                       (stat($dname))[2];
-               };
+               my $newdir = $tmp->{$old};
                my $have_old = -e $old;
                if (!$have_old && !defined($opt->{reshard})) {
                        die "failed to stat($old): $!";
@@ -57,11 +64,7 @@ sub commit_changes ($$$$) {
                                        die "rename $old => $new/old: $!\n";
                }
                rename($new, $old) or die "rename $new => $old: $!\n";
-               if ($have_old) {
-                       my $prev = "$old/old";
-                       remove_tree($prev) or
-                               die "failed to remove $prev: $!\n";
-               }
+               push @old_shard, "$old/old" if $have_old;
        }
 
        # trigger ->check_inodes in read-only daemons