BUG #2543: Performance delay acrros the same day

The following bug has been logged online:

Bug reference:      2543
Logged by:          Alaa El Gohary
Email address:      alaaelgohary@bftech.com.eg
PostgreSQL version: 7.4.12
Operating system:   FreeBSD 6.0
Description:        Performance delay acrros the same day
Details:

A query on the postgresql DB takes about 5 seconds and then it starts to
take more time till it reaches about 60 seconds by the end of the same day.
I tried vacuum but nothing changed the only thing that works is to dump the
DB ,drop and create a new one with the dump taken.
i need to know if there is any way to restore the performance back without
the need for drop and create
cause i can't do this accross the day