Re: [PATCH] Use idiomatic style for varlena structs

Tom Lane wrote:
> Jay Levitt<jay(dot)levitt(at)gmail(dot)com> writes:
>> I'm new to the codebase, but I think this patch reflects real-world usage;
>> the PostgreSQL code itself always calls the length field "vl_len_", and I
>> believe int32 is preferred over int4 (yes?)
>
> The point of calling it vl_len_ is that it should never be referenced by
> that name, so I'm not sure that propagating that name into user
> documentation is a good idea. I do agree with the part of this patch
> that recommends use of SET_VARSIZE.

Ah, ok. My confusion came from trying to build a new extension, using cube
as a baseline; cube (and all the other contrib extensions) use vl_len_, so I
saw a disconnect between the "int4 length" in the manual and the
"int32 vl_len_" in all the real-world examples I had.

My thought was that "vl_len_" *feels* more like a "this is mysterious and
I'd better not touch it - I'll use that macro", while "length" feels more
like something I might just set myself if I didn't know better. But maybe
not. Either way, the int32/int4 thing should be fixed.

> For context, the issues you're concerned about only matter when dealing
> with a toastable datatype (not all varlena types are toastable). The
> particular bit of docs here doesn't pretend to be explaining how to
> write toast-safe code. I think it might be better from an expository
> standpoint to cover that separately, rather than try to work it into the
> very first pass over the concepts.

Definitely; if anything, that's why I was favoring vl_len_. This is a magic
field. Do not touch the magic.

Jay