pg_dump filling up root directory

PostgreSQL Version: 7.3.4
Environment: Solaris (SunOS 5.9) Ultra-250

We do a nightly export-and-analyze of our databases, using these commands:

outfile=/data/export/${instance}~EXPORT~${ymd}.sql.tar
su - ${pg_user} -c "${pg_home}/bin/pg_dump -c -C -D -F t -f
${outfile} ${instance}"
gzip ${outfile}

su - ${pg_user} -c "${pg_home}/bin/vacuumdb -a -f -z -v " >
/usr/local/app/pgsql/log/vaclog.log 2>&1

where ${instance} is a database name;

During the dump, pg_dump writes something to the root directory (the
/data/export/ directory is on an external drive), and on occasion, whatever
is written to the root directory bloats, overfilling the root storage space:
from /var/adm/messages:
1 Apr 3 03:16:30 rutabaga -- MARK --
2 Apr 3 03:36:30 rutabaga -- MARK --
3 Apr 3 03:56:30 rutabaga -- MARK --
4 Apr 3 04:00:00 rutabaga MAINT: [ID 702911 local5.info]
/usr/local/gts/pgsql/maint/pgsql_daily.s
5 Apr 3 04:16:30 rutabaga -- MARK --
6 Apr 3 04:22:52 rutabaga ufs: [ID 845546 kern.notice] NOTICE:
alloc: /: file system full
7 Apr 3 04:36:30 rutabaga -- MARK --
8 Apr 3 04:56:30 rutabaga -- MARK --

We've done some research and seen some possible causes/solutions--we would
appreciate advice on the best approach (or better alternatives):

1) We suspect that pg_dump is using tmpfile while writting the export file:
is this true? and if so, how do we (can we?) control where tmpfile writes
during the export process?
2) We have seen references to piping the export to split to produce smaller
output files: how practical is this? will it counter the tmpfile bloating
(if that is what is happening)? if practical and effective, does anyone
know of a "best-practice" line count value to pass to split?

--

David Rickard
Software Engineer
The GTS Companies
A TechBooks Company

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