3 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/public-inbox-v1-format.pod b/Documentation/public-inbox-v1-format.pod
index 2a6b8d3c..3b0e70e1 100644
--- a/Documentation/public-inbox-v1-format.pod
+++ b/Documentation/public-inbox-v1-format.pod
@@ -134,6 +134,10 @@ Since SCHEMA_VERSION 15 and the development of the v2 format,
  the "overview" DB also exists in the xapian directory for v1
  repositories.  See L<public-inbox-v2-format(5)/OVERVIEW DB>
  
+Our use of the L</OVERVIEW DB> requires Xapian document IDs to
+remain stable.  Thus, use of L<xapian-compact(1)> and
+L<copydatabase(8)> require the use of C<--no-renumber> switch.
+
  =item $GIT_DIR/ssoma.index
  
  This file is no longer used or created by public-inbox, but it is
diff --git a/Documentation/public-inbox-v2-format.pod b/Documentation/public-inbox-v2-format.pod
index 7dfe3296..bc58074e 100644
--- a/Documentation/public-inbox-v2-format.pod
+++ b/Documentation/public-inbox-v2-format.pod
@@ -117,6 +117,10 @@ Rotational storage devices are NOT recommended for indexing of
  large mail archives; but are fine for backup and usable for
  small instances.
  
+Our use of the L</OVERVIEW DB> requires Xapian document IDs to
+remain stable.  Thus, use of L<xapian-compact(1)> and
+L<copydatabase(8)> require the use of C<--no-renumber> switch.
+
  =head2 OVERVIEW DB
  
  Towards the end of v2 development, it became apparent Xapian did
diff --git a/script/public-inbox-compact b/script/public-inbox-compact
index d22e4032..395eec37 100755
--- a/script/public-inbox-compact
+++ b/script/public-inbox-compact
@@ -51,6 +51,8 @@ sub commit_changes ($$$) {
          $im->lock_release;
          remove_tree("$old/old") or die "failed to remove $old/old: $!\n";
  }
+
+# we rely on --no-renumber to keep docids synched to NNTP
  my @compact = qw(xapian-compact --no-renumber);
  if ($v == 2) {
          require PublicInbox::V2Writable;