Re: OCTET_LENGTH is wrong

Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> writes:
> On Sun, 18 Nov 2001, Tom Lane wrote:
>> I presume that where you want to come out is OCTET_LENGTH = uncompressed
>> length in the server's encoding ... but so far no one has really made
>> a convincing argument why that answer is better or more spec-compliant
>> than any other answer. In particular, it's not obvious to me why
>> "number of bytes we're actually using on disk" is wrong.

> I'm not sure, but if we say that the on disk representation is the
> value of the character value expression whose size is being checked,
> wouldn't that be inconsistent with the other uses of the character value

Yeah, it would be and is. In fact, the present code has some
interesting behaviors: if foo.x is a text value long enough to be
toasted, then you get different results from

SELECT OCTET_LENGTH(x) FROM foo;

SELECT OCTET_LENGTH(x || '') FROM foo;

since the result of the concatenation expression won't be compressed.

I'm not actually here to defend the existing code; in fact I believe the
XXX comment on textoctetlen questioning its correctness is mine. What
I am trying to point out is that the spec is so vague that it's not
clear what the correct answer is.

regards, tom lane