Re: texteq/byteaeq: avoid detoast [REVIEW]

On Mon, Jan 17, 2011 at 09:13, Itagaki Takahiro
<itagaki(dot)takahiro(at)gmail(dot)com> wrote:
> 2011/1/17 KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)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.

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 Magnus Hagander
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