problems with new vacuum (??)

Over the last two days I have been struggling with running vacuum on a
7.2b4 database that is running in a production environment. This was
essentially the first time I ran vacuum on this database since it was
upgraded to 7.2. This database is characterized by one large table that
has many inserts and deletes, however generally contains zero rows. So
over the course of the last few weeks this table had grown in size to
about 2.5G (or more correctly the corresponding toast table grew that
large).

So the first problem I had was that the vaccum (regular vacuum not full
vacuum) took a very long time on this table (2+ hours). Now I would
expect it to take a while, so that in and of itself isn't a problem.
But while this vacuum was running the rest of the system was performing
very poorly. Opperations that usually are subsecond, where taking
minutes to complete. At first I thought there was some sort of locking
problem, but these opperations did complete, but after a very long time.

In looking at the log files from this time, I noticed that while the
vacuum process was running, there were a lot of the following messages
in the log file:

2001-12-31 22:16:40 [20655] DEBUG: recycled transaction log file
000000010000009A

The interesting thing (at least in my mind) is that these messages were
produced by all of the other postgres processes, not by the vacuum
process. (And by the way what do they mean?)

The second issue I noticed was that the vacuum process later just hung.
Since I didn't think the new vacuum was supposed to hang (since I
thought it tried a best effort and if it couldn't lock something it
would just skip it).

2001-12-31 22:18:04 [19945] NOTICE: --Relation xyf_files--
2001-12-31 22:21:51 [20673] DEBUG: recycled transaction log file
000000010000009C
2001-12-31 22:21:51 [20673] DEBUG: recycled transaction log file
000000010000009D
2001-12-31 22:21:51 [20673] DEBUG: recycled transaction log file
000000010000009B
2001-12-31 22:31:54 [20711] DEBUG: recycled transaction log file
000000010000009F
2001-12-31 22:31:54 [20711] DEBUG: recycled transaction log file
000000010000009E
2002-01-01 07:30:58 [19945] ERROR: Query was cancelled.

It hung until I cancelled the vacuum with a ^c. So then I tried to
rerun the vacuum and it hung in the same spot, this time for 1.5 hours
before I killed it.

Thinking that maybe there was some sort of problem with this table I ran
a vacuum full (after restarting the database to make sure no other
processes would be locking the full vacuum) and it ran to completion.

Now after the full vacuum the the regular vacuum runs almost instantly
with no further problems.

Is there a bug here, I don't know, but I thought it was interesting
enough to post what I just saw.

thanks,
--Barry