"Leaking" disk space

[Dan Thomas]

Hi Guys,

We're seeing a problem with some of our FreeBSD/PostgreSQL servers
"leaking" quite significant amounts of disk space:

    > df -h /usr/local/pgsql/
    Filesystem       Size    Used   Avail Capacity  Mounted on
    /dev/mfid1s1d    1.1T    772G    222G    78%    /usr/local/pgsql

    > du -sh /usr/local/pgsql/
    741G    /usr/local/pgsql/

Stopping Postgres doesn't fix it, but rebooting does which points at
the OS rather than PG to me. However, the leak is only apparent in the
dedicated pgsql partition, and only on our database servers, so
PostgreSQL seems to at least be involved. The partition itself is a
relatively standard UFS partition:

    > grep /usr/local/pgsql /etc/fstab
    /dev/mfid1s1d   /usr/local/pgsql    ufs   rw   2   2

    > tunefs -p /usr/local/pgsql/
    tunefs: POSIX.1e ACLs: (-a)                                disabled
    tunefs: NFSv4 ACLs: (-N)                                   disabled
    tunefs: MAC multilabel: (-l)                               disabled
    tunefs: soft updates: (-n)                                 enabled
    tunefs: gjournal: (-J)                                     disabled
    tunefs: trim: (-t)                                         disabled
    tunefs: maximum blocks per file in a cylinder group: (-e)  2048
    tunefs: average file size: (-f)                            16384
    tunefs: average number of files in a directory: (-s)       64
    tunefs: minimum percentage of free space: (-m)             8%
    tunefs: optimization preference: (-o)                      time
    tunefs: volume label: (-L)

LSOF isn't showing any open files:

    > lsof +L /usr/local/pgsql/ | awk '{ print $8 }' | grep 0 | wc -l
    0

We're not creating filesystem snapshots:

    > find /usr/local/pgsql/ -flags snapshot
    >

Not all of our servers are leaking space, it's only the more
recently-installed systems. Here's a quick breakdown of versions:

    FreeBSD   PostgreSQL   Leaking?
    8.0       8.4.4        no
    8.2       9.0.4        no
    8.3       9.1.4        yes
    8.3       9.2.3        yes
    9.1       9.2.3        yes

Any ideas what's going on here, or where we could start debugging?

Thanks,

Dan