BUG #5284: Postgres CPU 100% and worker took too long to start; cancelled... Systemdown

The following bug has been logged online:

Bug reference: 5284
Logged by: azuneko
Email address: azuneko(at)hotmail(dot)com
PostgreSQL version: 8.3.3
Operating system: FreeBSD7.0.2
Description: Postgres CPU 100% and worker took too long to start;
cancelled... Systemdown
Details:

Hello,

I have the following 2 problems.
It would be appreciated if you give me some information such as the way to
avoid them.(Or if those problems are already known and fixed, could you
please tell me what version I should apply.)

1,CPU utilization of postgres reaches 100%.

I excuted "top" command and sometimes found that CPU utilization of postgres
process reached 100% or almost 100%. (This is similar to the problem that
was posted at
http://archives.free.net.ph/message/20081104.074244.6e0dbcde.ja.html.)
What might be the cause?

2. The following warning can be seen in the postgres log.
WARNING: worker took too long to start; cancelled

After this warning firstly appears in the log, the same warining message
seems to be repeated. And if you leave this state as it is, the OS freezes
before long. I guess this event happens because the daemons related to
postgres (such as vacuum and autovacuum) won't release the shared memory and
exclusively keep using it. Am I correct?

Those 2 problems are confirmed to happen at least under the following
conditions;
Software
-OS : FreeBSD 7.0.2
-Postgres version : 8.3.3
Hardware
-Disk configuration : RAID5 (MegaCLI)
-CPU : Xeon2.4

Thank you.