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.

Well, if the standard is unclear, we should assume to return the most
reasonable answer, which has to be non-compressed length.

In multibyte encodings, when we started returning length() in
_characters_ instead of bytes, I assumed the major use for octet_length
was to return the number of bytes needed to hold the value on the client
side.

In single byte encodings, octet_length is the same as length() so
returning a compressed length may make sense, but I don't think we want
different meanings for the function for single and multi-byte encodings.

I guess the issue is that for single-byte encodings, octet_length is
pretty useless because it is the same as length, but for multi-byte
encodings, octet_length is invaluable and almost has to return
non-compress bytes because uncompressed is that the client sees.

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