[Bug 1411633] Re: man-db's manipulation of index.db mtime timestamp interferes with incremental backups

[Colin Watson]

This is a consequence of the poor layout noted in this comment in
purge_missing:

        if (will_run_mandb)
                /* Reset mtime to avoid confusing mandb into not running.
                 * TODO: It would be better to avoid this by only opening
                 * the database once between here and mandb.
                 */
                MYDBM_SET_TIME (dbf, db_mtime);

There are some situations where a later update_db will not actually
modify the database and update the mtime, and in this situation
purge_missing may have updated the database but reset the mtime to its
previous value.  The reorganisation implied by this comment would fix
this.

** Changed in: man-db (Ubuntu)
       Status: New => Triaged

** Changed in: man-db (Ubuntu)
   Importance: Undecided => High

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https://bugs.launchpad.net/bugs/1411633

Title:
  man-db's manipulation of index.db mtime timestamp interferes with
  incremental backups

Status in man-db package in Ubuntu:
  Triaged

Bug description:
  It appears that since version 2.7.0, man-db manipulates the mtime
  timestamp of /var/cache/man/de/index.db in a way that the content may
  change, while the timestamp is reset to its previous value (see
  attachment).

  See https://lists.ubuntu.com/archives/foundations-
  bugs/2014-September/209326.html

  This interferes with incremental backups which pick up files via their
  modification timestamps. Such backups will miss updated files which do
  not have their mtime timestamps changed accordingly. Automated
  comparisons between such backups and (btrfs snapshots of) their source
  data will fail. The integrity of such backups cannot be guaranteed.

  Release: Ubuntu 14.10
  Package: man-db 2.7.0.2-2

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