alter table set tablespace over nfs getting stuck

Good Day:

I understand that it is undesireable to run a database over NFS. However,
due to the shortage of local space on my machine, I had to utilize NFS space
on another machine as an additional tablespace. The tables got created fine
on the NFSed tablespace. Now that I have some more local space on my
machine, I wanted to move the tables from the remove tablespace "ts2" to the
default tablespace "pg_default". Postgres seems to not like that a whole
lot.

The "alter table" works fine for some tables and then it hangs. The relative
location of this hung-status changes from one run to the next. The hung
request does not want to cancel or die (via kill without any flags) either.
It also consumes a good chunk of the CPU cycles. It feels like there is some
sort of a spin lock which got stuck. Additional "alter table" requests in
separate sessions continue to work fine. There are no NFS errors logged. The
tables are a couple hundred megabytes each. My NFSed directory is mounted
"rw,tcp,hard,intr,rsize=8192,wsize=8192". And I am running Postgres 8.1 on a
dual processor 64-bit AMD.

Are there certain dos and don'ts of NFS file space usage in postgres? Is
there a way of killing the stuck clients?

Thanks.
PS: From the looks of the data files belonging to the table, it seems that
the entire data had been copied and then postgres got stuck.