On Mon, Jan 17, 2011 at 09:13, Itagaki Takahiro <itagaki.takah...@gmail.com> wrote: > 2011/1/17 KaiGai Kohei <kai...@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.
Yeah, that might be a bad tradeoff. I wonder if we can trust the *equality* test, but not the inequality? E.g. if compressed(A) == compressed(B) we know they're the same, but if compressed(A) != compressed(B) we don't know they're not they still might be. I guess with two different versions or even completely different algorithms we could end up with exactly the same compressed value for different plaintexts (it's not a cryptographic hash after all), so that's probably not an acceptable comparison either. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers