You can diminish the size of the journal by means of these commands:
This will retain the most recent 100M of data.
will delete everything but the last 10 days.
--vacuum-size=, --vacuum-time=, --vacuum-files=
Removes the oldest archived journal files until the disk space they use falls below the specified size (specified with the
usual "K", "M", "G" and "T" suffixes), or all archived journal files
contain no data older than the specified timespan (specified with the
usual "s", "m", "h", "days", "months", "weeks" and "years" suffixes),
or no more than the specified number of separate journal files remain.
Note that running --vacuum-size= has only an indirect effect on the
output shown by --disk-usage, as the latter includes active journal
files, while the vacuuming operation only operates on archived journal
files. Similarly, --vacuum-files= might not actually reduce the number
of journal files to below the specified number, as it will not remove
active journal files.
--vacuum-size=, --vacuum-time= and --vacuum-files= may be combined in a single invocation to enforce any combination of a size, a time
and a number of files limit on the archived journal files. Specifying
any of these three parameters as zero is equivalent to not enforcing
the specific limit, and is thus redundant.
These three switches may also be combined with --rotate into one
command. If so, all active files are rotated first, and the requested
vacuuming operation is executed right after. The rotation has the
effect that all currently active files are archived (and potentially
new, empty journal files opened as replacement), and hence the
vacuuming operation has the greatest effect as it can take all log data written so far into account.