[systemd-bugs] [Bug 72601] New: journalctl -b -0 -D <nfs mount>/.../journal: very slow startup on slow NFS mount

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=72601

          Priority: medium
            Bug ID: 72601
          Assignee: systemd-bugs at lists.freedesktop.org
           Summary: journalctl -b -0 -D <nfs mount>/.../journal: very slow
                    startup on slow NFS mount
        QA Contact: systemd-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: a.c.kalker at gmail.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: general
           Product: systemd

Investigating why a diskless client (booted over NFS) crashed, I noticed that:

$ mount -o nolock,ro <nfs-server>:/nfs/<clientroot> mnt
$ journalctl -b -0 -D mnt/var/log/journal

took almost 6 seconds before showing the log.
The NFS 'server' is a consumer grade router with a hard disk attached to its
USB port, resulting in reasonably slow transfer speeds, but which are otherwise
acceptable for its intended purpose.

>From experience with a few other systems, startup time for journalctl increases
as the number of boots recorded and the journal size increases. I believe this
may be due to the high number of disk accesses required to find the beginning
of entries pertaining to the last boot in the journal.

This bug report is a request for improving the access speed of specific boot
journal entries.

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