TOAST behavior in 8.3 and 8.4

I have a table with a text column, wherein most values range between 800
and 1700 bytes. The data should be highly compressible, however these
values appear to be too small to trigger the TOAST mechanism - I
understand the default value of TOAST_TUPLE_THRESHOLD is about 2kb.

This table is by far the largest in our database (1006450 rows;
pg_relation_size() gives 1580 MB), and I am keen to get the data
compressed. We compile from source and are currently running 8.3.10.
Based on some discussions I found in the archives, I thought it might be
worthwhile to lower TOAST_TUPLE_THRESHOLD and rebuild.

However, I checked to see whether the behavior of TOAST had been changed
in 8.4, since I am hoping to upgrade soon. I found the following
comment in the release notes:

"Consider TOAST compression on values as short as 32 bytes (previously
256 bytes)"

I don't understand what that '256 bytes' refers to. That is a far cry
from 2kb. I would be grateful if anyone can fill in the evident gap in
my knowledge here.

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Thank you,

Lewis Kapell
Computer Operations
Seton Home Study School