+ if (! message->modified)
+ return;
+
+ /* Update the last modification of this message. */
+ if (message->notmuch->features & NOTMUCH_FEATURE_LAST_MOD)
+ /* sortable_serialise gives a reasonably compact encoding,
+ * which directly translates to reduced IO when scanning the
+ * value stream. Since it's built for doubles, we only get 53
+ * effective bits, but that's still enough for the database to
+ * last a few centuries at 1 million revisions per second. */
+ message->doc.add_value (NOTMUCH_VALUE_LAST_MOD,
+ Xapian::sortable_serialise (
+ _notmuch_database_new_revision (
+ message->notmuch)));
+