lib/PublicInbox/LeiToMail.pm  | 32 ++++++++++++++++++++++++++++----
 lib/PublicInbox/LeiXSearch.pm | 26 ++++++++++++++++----------
 lib/PublicInbox/NetReader.pm  |  9 +++++++--

diff --git a/lib/PublicInbox/LeiToMail.pm b/lib/PublicInbox/LeiToMail.pm
index b5d560c7b735a80142536b6e003acdd227005e0c..6efd398a76652c880637b17d0fe0194f5b1fa06a 100644
--- a/lib/PublicInbox/LeiToMail.pm
+++ b/lib/PublicInbox/LeiToMail.pm
@@ -19,6 +19,7 @@ use Symbol qw(gensym);
 use IO::Handle; # ->autoflush
 use Fcntl qw(SEEK_SET SEEK_END O_CREAT O_EXCL O_WRONLY);
 use Errno qw(EEXIST ESPIPE ENOENT EPIPE);
+use Digest::SHA qw(sha256_hex);
 my ($maildir_each_file);
 
 # struggles with short-lived repos, Gcf2Client makes little sense with lei;
@@ -269,7 +270,15 @@ 	}
 }
 
 sub _augment_file { # maildir_each_file cb
-	my ($f, $lei) = @_;
+	my ($f, $lei, $mod, $shard) = @_;
+	if ($mod) {
+		# can't get dirent.d_ino w/ pure Perl, so we extract the OID
+		# if it looks like one:
+		my $hex = $f =~ m!\b([a-f0-9]{40,})[^/]*\z! ?
+				$1 : sha256_hex($f);
+		my $recno = hex(substr($hex, 0, 8));
+		return if ($recno % $mod) != $shard;
+	}
 	my $eml = PublicInbox::InboxWritable::eml_from_path($f) or return;
 	_augment($eml, $lei);
 }
@@ -421,7 +430,9 @@ 	my $dst = $lei->{ovv}->{dst};
 	if ($lei->{opt}->{augment}) {
 		my $dedupe = $lei->{dedupe};
 		if ($dedupe && $dedupe->prepare_dedupe) {
-			$maildir_each_file->($dst, \&_augment_file, $lei);
+			my ($mod, $shard) = @{$self->{shard_info} // []};
+			$maildir_each_file->($dst, \&_augment_file,
+						$lei, $mod, $shard);
 			$dedupe->pause_dedupe;
 		}
 	} else { # clobber existing Maildir
@@ -516,11 +527,24 @@ sub ipc_atfork_child {
 	my ($self) = @_;
 	my $lei = delete $self->{lei};
 	$lei->lei_atfork_child;
-	if ($self->{-wq_worker_nr} == 0) {
+	my $aug;
+	if (lock_free($self)) {
+		my $mod = $self->{-wq_nr_workers};
+		my $shard = $self->{-wq_worker_nr};
+		if (my $nwr = $lei->{nwr}) {
+			$nwr->{shard_info} = [ $mod, $shard ];
+		} else { # Maildir (MH?)
+			$self->{shard_info} = [ $mod, $shard ];
+		}
+		$aug = '+'; # incr_post_augment
+	} elsif ($self->{-wq_worker_nr} == 0) {
+		$aug = '.'; # do_post_augment
+	}
+	if ($aug) {
 		local $0 = 'do_augment';
 		eval { do_augment($self, $lei) };
 		$lei->fail($@) if $@;
-		pkt_do($lei->{pkt_op_p}, '.') == 1 or
+		pkt_do($lei->{pkt_op_p}, $aug) == 1 or
 					die "do_post_augment trigger: $!";
 	}
 	if (my $zpipe = delete $lei->{zpipe}) {
diff --git a/lib/PublicInbox/LeiXSearch.pm b/lib/PublicInbox/LeiXSearch.pm
index 524f4d1ceb157328726f0a4ce7d759befe7d2fa2..e982165f8014395e0b37fbab5a78eaee3eb45eba 100644
--- a/lib/PublicInbox/LeiXSearch.pm
+++ b/lib/PublicInbox/LeiXSearch.pm
@@ -331,23 +331,28 @@ }
 
 sub do_post_augment {
 	my ($lei) = @_;
-	my $l2m = $lei->{l2m};
+	my $l2m = $lei->{l2m} or die 'BUG: unexpected do_post_augment';
 	my $err;
-	if ($l2m) {
-		eval { $l2m->post_augment($lei) };
-		$err = $@;
-		if ($err) {
-			if (my $lxs = delete $lei->{lxs}) {
-				$lxs->wq_kill;
-				$lxs->wq_close(0, undef, $lei);
-			}
-			$lei->fail("$err");
+	eval { $l2m->post_augment($lei) };
+	$err = $@;
+	if ($err) {
+		if (my $lxs = delete $lei->{lxs}) {
+			$lxs->wq_kill;
+			$lxs->wq_close(0, undef, $lei);
 		}
+		$lei->fail("$err");
 	}
 	if (!$err && delete $lei->{early_mua}) { # non-augment case
 		$lei->start_mua;
 	}
 	close(delete $lei->{au_done}); # triggers wait_startq in lei_xsearch
+}
+
+sub incr_post_augment { # called whenever an l2m shard finishes
+	my ($lei) = @_;
+	my $l2m = $lei->{l2m} or die 'BUG: unexpected incr_post_augment';
+	return if ++$lei->{nr_post_augment} != $l2m->{-wq_nr_workers};
+	do_post_augment($lei);
 }
 
 my $MAX_PER_HOST = 4;
@@ -392,6 +397,7 @@ 	my $ops = {
 		'|' => [ $lei->can('sigpipe_handler'), $lei ],
 		'!' => [ $lei->can('fail_handler'), $lei ],
 		'.' => [ \&do_post_augment, $lei ],
+		'+' => [ \&incr_post_augment, $lei ],
 		'' => [ \&query_done, $lei ],
 		'mset_progress' => [ \&mset_progress, $lei ],
 		'x_it' => [ $lei->can('x_it'), $lei ],
diff --git a/lib/PublicInbox/NetReader.pm b/lib/PublicInbox/NetReader.pm
index 4c4124913ec64b3c488bf385841950d3571e0e82..0956d5dad6517509194e093fcc4db9efd74e9f64 100644
--- a/lib/PublicInbox/NetReader.pm
+++ b/lib/PublicInbox/NetReader.pm
@@ -363,8 +363,11 @@ 			"E: $uri strangely, UIDVALIDLITY matches ($l_uidval)\n";
 	}
 	return if $l_uid >= $r_uid; # nothing to do
 	$l_uid ||= 1;
-
-	warn "# $uri fetching UID $l_uid:$r_uid\n" unless $self->{quiet};
+	my ($mod, $shard) = @{$self->{shard_info} // []};
+	unless ($self->{quiet}) {
+		my $m = $mod ? " [(UID % $mod) == $shard]" : '';
+		warn "# $uri fetching UID $l_uid:$r_uid$m\n";
+	}
 	$mic->Uid(1); # the default, we hope
 	my $bs = $self->{imap_opt}->{$sec}->{batch_size} // 1;
 	my $req = $mic->imap4rev1 ? 'BODY.PEEK[]' : 'RFC822.PEEK';
@@ -391,6 +394,8 @@
 		$l_uid = $uids->[-1] + 1; # for next search
 		my $last_uid;
 		my $n = $self->{max_batch};
+
+		@$uids = grep { ($_ % $mod) == $shard } @$uids if $mod;
 		while (scalar @$uids) {
 			my @batch = splice(@$uids, 0, $bs);
 			$batch = join(',', @batch);