-designed for "v2" inboxes. It combines multiple Xapian
-partitions into one to reduce space overhead after an initial
-mass import (using multiple partitions) is done.
+which locks the inbox and prevents other processes such as
+L<public-inbox-watch(1)> or L<public-inbox-mda(1)> from
+writing while it operates.
+
+It enforces the use of the C<--no-renumber> option of
+L<xapian-compact(1)> which is required to work with the
+rest of the public-inbox search code.
+
+This command is rarely needed for active inboxes.
+
+Using the C<--compact> option of L<public-inbox-index(1)>
+is recommended, instead, and only when doing a C<--reindex>.
+
+=head1 OPTIONS
+
+=over
+
+=item --all
+
+Compact all inboxes configured in ~/.public-inbox/config.
+This is an alternative to specifying individual inboxes directories
+on the command-line.