MANIFEST                     |  2 ++
 lib/PublicInbox/ExtSearch.pm | 40 ++++++++++++++++++++++++++++++++++++++++
 lib/PublicInbox/Search.pm    |  4 ++--
 t/extsearch.t                | 11 +++++++++++

diff --git a/MANIFEST b/MANIFEST
index b6a681e9b533e50971ae416a25ef7f9d94a6eb10..60055d2b10b1d61b9cd5a2018a5acc34f2fc0979 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -121,6 +121,7 @@ lib/PublicInbox/Emergency.pm
 lib/PublicInbox/Eml.pm
 lib/PublicInbox/EmlContentFoo.pm
 lib/PublicInbox/ExtMsg.pm
+lib/PublicInbox/ExtSearch.pm
 lib/PublicInbox/FakeInotify.pm
 lib/PublicInbox/Feed.pm
 lib/PublicInbox/Filter/Base.pm
@@ -269,6 +270,7 @@ t/eml.t
 t/eml_content_disposition.t
 t/eml_content_type.t
 t/epoll.t
+t/extsearch.t
 t/fail-bin/spamc
 t/fake_inotify.t
 t/feed.t
diff --git a/lib/PublicInbox/ExtSearch.pm b/lib/PublicInbox/ExtSearch.pm
new file mode 100644
index 0000000000000000000000000000000000000000..9bbe785702a4142de855b3f0cc4af2eea802f6e6
--- /dev/null
+++ b/lib/PublicInbox/ExtSearch.pm
@@ -0,0 +1,40 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# Read-only external (detached) index for cross inbox search.
+# This is a read-only counterpart to PublicInbox::ExtSearchIdx
+package PublicInbox::ExtSearch;
+use strict;
+use v5.10.1;
+use PublicInbox::Over;
+
+# for ->reopen, ->mset, ->mset_to_artnums
+use parent qw(PublicInbox::Search);
+
+sub new {
+	my (undef, $topdir) = @_;
+	bless {
+		topdir => $topdir,
+		# xpfx => 'ei15'
+		xpfx => "$topdir/ei".PublicInbox::Search::SCHEMA_VERSION
+	}, __PACKAGE__;
+}
+
+# overrides PublicInbox::Search::_xdb
+sub _xdb {
+	my ($self) = @_;
+	$self->_xdb_sharded($self->{xpfx});
+}
+
+# same as per-inbox ->over, for now...
+sub over {
+	my ($self) = @_;
+	$self->{over} //= PublicInbox::Over->new("$self->{xpfx}/over.sqlite3");
+}
+
+sub git {
+	my ($self) = @_;
+	$self->{git} //= PublicInbox::Git->new("$self->{topdir}/ALL.git");
+}
+
+1;
diff --git a/lib/PublicInbox/Search.pm b/lib/PublicInbox/Search.pm
index 6346d78838e38301e7306e6b5222a35ca5b8a365..5a57657ff4da5b1332afe8db5ed39b35c06f7d4e 100644
--- a/lib/PublicInbox/Search.pm
+++ b/lib/PublicInbox/Search.pm
@@ -245,9 +245,9 @@ }
 
 sub xdb ($) {
 	my ($self) = @_;
-	$self->{xdb} ||= do {
+	$self->{xdb} //= do {
 		load_xapian();
-		_xdb($self);
+		$self->_xdb;
 	};
 }
 
diff --git a/t/extsearch.t b/t/extsearch.t
new file mode 100644
index 0000000000000000000000000000000000000000..7687f5f01a3ee222488632d366cb18092bf04ae4
--- /dev/null
+++ b/t/extsearch.t
@@ -0,0 +1,11 @@
+#!perl -w
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+use strict;
+use Test::More;
+use PublicInbox::TestCommon;
+require_git(2.6);
+require_mods(qw(DBD::SQLite Search::Xapian));
+use_ok 'PublicInbox::ExtSearch';
+
+done_testing;