Documentation/public-inbox-extindex.pod | 22 ++++++++++++++++++++++
 lib/PublicInbox/ExtSearchIdx.pm         |  6 +++---
 script/public-inbox-extindex            |  9 ++++++---
 t/extsearch.t                           |  5 +++++

diff --git a/Documentation/public-inbox-extindex.pod b/Documentation/public-inbox-extindex.pod
index 2e2e6383b79b35c31f7be30ed1daa7996a1674dd..a0fca83c6255b1bcfa5a89270501dba164004cdb 100644
--- a/Documentation/public-inbox-extindex.pod
+++ b/Documentation/public-inbox-extindex.pod
@@ -40,6 +40,28 @@ (C<xap15> or C<xapian15>) directories removed.  For multiple
 public-inboxes where cross-posting is common, this allows
 significant space savings on Xapian indices.
 
+=item --gc
+
+Perform garbage collection instead of indexing.  Use this if
+inboxes are removed from the extindex, or if messages are
+purged or removed from some inboxes.
+
+=item --reindex
+
+Forces a re-index of all messages in the extindex.  This can be
+used for in-place upgrades and bugfixes while read-only server
+processes are utilizing the index.  Keep in mind this roughly
+doubles the size of the already-large Xapian database.
+
+The extindex locks will be released roughly every 10s to
+allow L<public-inbox-mda(1)> and L<public-inbox-watch(1)>
+processes to write to the extindex.
+
+=item --fast
+
+Used with C<--reindex>, it will only look for new and stale
+entries and not touch already-indexed messages.
+
 =back
 
 =head1 FILES
diff --git a/lib/PublicInbox/ExtSearchIdx.pm b/lib/PublicInbox/ExtSearchIdx.pm
index 7cc8dd952559d17b3c5c600a7ac8155547ad34ce..20c4cf7807eae9cb152b9760c9ede22bfdc95595 100644
--- a/lib/PublicInbox/ExtSearchIdx.pm
+++ b/lib/PublicInbox/ExtSearchIdx.pm
@@ -811,7 +811,7 @@ 	my $ekey = $ibx->eidx_key;
 	local $sync->{-regen_fmt} =
 			"$ekey checking unseen %u/".$ibx->over->max."\n";
 	${$sync->{nr}} = 0;
-
+	my $fast = $sync->{-opt}->{fast};
 	while (scalar(@{$msgs = $ibx->over->query_xover($beg, $end)})) {
 		${$sync->{nr}} = $beg;
 		$beg = $msgs->[-1]->{num} + 1;
@@ -835,7 +835,7 @@ 			# index messages which were totally missed
 			# the first time around ASAP:
 			if (scalar(@$docids) == 0) {
 				reindex_unseen($self, $sync, $ibx, $xsmsg);
-			} else { # already seen, reindex later
+			} elsif (!$fast) { # already seen, reindex later
 				for my $r (@$docids) {
 					$self->{oidx}->eidxq_add($r->[0]);
 				}
@@ -853,7 +853,7 @@ 	my $pr = $sync->{-opt}->{-progress};
 	my $fetching;
 	my $ekey = $ibx->eidx_key;
 	local $sync->{-regen_fmt} =
-			"$ekey check stale/missing %u/".$ibx->over->max."\n";
+			"$ekey checking stale/missing %u/".$ibx->over->max."\n";
 	${$sync->{nr}} = 0;
 	do {
 		if (checkpoint_due($sync)) {
diff --git a/script/public-inbox-extindex b/script/public-inbox-extindex
index 1572a1d23d82dad663a81956c3b95ea955ee13f0..c63f5dc26fd29527319987ce160807f5e9f2879d 100755
--- a/script/public-inbox-extindex
+++ b/script/public-inbox-extindex
@@ -18,6 +18,8 @@   --batch-size=BYTES  flush changes to OS after a given number of bytes
   --max-size=BYTES    do not index messages larger than the given size
   --gc                perform garbage collection instead of indexing
   --dedupe[=MSGID]    fix prior deduplication errors (may be repeated)
+  --reindex           index previously indexed inboxes
+  --fast              only reindex unseen/stale messages
   --verbose | -v      increase verbosity (may be repeated)
   --dry-run | -n      dry-run on --dedupe
 
@@ -26,7 +28,7 @@ See public-inbox-extindex(1) man page for full documentation.
 EOF
 my $opt = { quiet => -1, compact => 0, fsync => 1, scan => 1 };
 GetOptions($opt, qw(verbose|v+ reindex rethread compact|c+ jobs|j=i
-		fsync|sync!
+		fsync|sync! fast
 		indexlevel|index-level|L=s max_size|max-size=s
 		batch_size|batch-size=s
 		dedupe:s@ gc commit-interval=i watch scan! dry-run|n
@@ -59,9 +61,10 @@ 	}
 } else {
 	@ibxs = PublicInbox::Admin::resolve_inboxes(\@ARGV, $opt, $cfg);
 }
-if ($opt->{'dry-run'} && !$opt->{dedupe}) {
+$opt->{'dry-run'} && !$opt->{dedupe} and
 	die "E: --dry-run only affects --dedupe\n";
-}
+$opt->{fast} && !$opt->{reindex} and
+	die "E: --fast only affects --reindex\n";
 
 PublicInbox::Admin::require_or_die(qw(-search));
 PublicInbox::Config::json() or die "Cpanel::JSON::XS or similar missing\n";
diff --git a/t/extsearch.t b/t/extsearch.t
index ca586f61c29f5ecab581d56a1dc7a1bdb71e51c5..896e270414bd8eff0e909fe2fbdacf291bec33cf 100644
--- a/t/extsearch.t
+++ b/t/extsearch.t
@@ -336,6 +336,11 @@ 		'stale message has no xref3');
 	$es->{xdb}->reopen;
 	$mset = $es->mset("mid:$new->{mid}");
 	is($mset->size, 0, 'stale mid gone Xapian');
+
+	ok(run_script([qw(-extindex --reindex --all --fast), "$home/extindex"],
+			undef, $opt), '--reindex w/ --fast');
+	ok(!run_script([qw(-extindex --all --fast), "$home/extindex"],
+			undef, $opt), '--fast alone makes no sense');
 }
 
 if ('reindex catches content bifurcation') {