2011/1/17 KaiGai Kohei <kaigai@ak.jp.nec.com>:
> Are you talking about an idea to apply toast id as an alternative key?
No, probably. I'm just talking about whether "diff -q A.txt B.txt" and
"diff -q A.gz B.gz" always returns the same result or not.
... I found it depends on version of gzip. So, if we use such logic,
we cannot improve toast compression logic because the data is migrated
by pg_upgrade.
> I did similar idea to represent security label on user tables for row
> level security in the v8.4/9.0 based implementation. Because a small
> number of security labels are shared by massive tuples, it is waste of
> space if we have all the text data being toasted individually, not only
> performance loss in toast/detoast.
It looks the same issue as large object rather than the discussion here.
We have vacuumlo in contrib to solve the issue. So, we could have
vacuumlo-like special sweeping logic for the security label table.
--
Itagaki Takahiro
