Re: OCTET_LENGTH is wrong

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> I noticed OCTET_LENGTH will return the size of the data after TOAST may
> have compressed it. While this could be useful information, this
> behaviour has no basis in the SQL standard and it's not what is
> documented. Moreover, it eliminates the standard useful behaviour of
> OCTET_LENGTH, which is to show the length in bytes of a multibyte string.

I wondered about that too, the first time I noticed it. On the other
hand, knowing the compressed length is kinda useful too, at least for
hacking and DBA purposes. (One might also like to know whether a value
has been moved out of line, which is not currently determinable.)

I don't want to force an initdb at this stage, at least not without
compelling reason, so adding more functions right now is not feasible.
Maybe a TODO item for next time.

That leaves us with the question whether to change OCTET_LENGTH now
or leave it for later. Anyone?

BTW, I noticed that textlength() is absolutely unreasonably slow when
MULTIBYTE is enabled --- yesterday I was trying to profile TOAST
overhead, and soon discovered that what I was looking at was nothing
but pg_mblen() calls. It really needs a short-circuit path for
single-byte encodings.

regards, tom lane