Re: how to understand these macro defines such as ObjectIdAttributeNumber in sysattr.h?

hi, Michael
thanks a lot! your reminding lead me go a step forward!
the 7 attributes are system attributes of some table such as pg_class,
pg_type. but now I have a new question:

where and when using these system attributes?

2014-08-18 15:57 GMT+08:00 Michael Paquier <michael(dot)paquier(at)gmail(dot)com>:

> On Mon, Aug 18, 2014 at 4:42 PM, 土卜皿 <pengcz(dot)nwpu(at)gmail(dot)com> wrote:
> > Recently, for understanding postgresql's optimizer, I read and debug
> the
> > source code. these two days, I read these macros in sysattr.h:
> >
> > ...
> > #define ObjectIdAttributeNumber (-2)
> > ...
> >
> > and the relative codes, but I still did not know why authors designed
> them
> > like that, especially the value '-2' ?
> >
> > what should I do if I want to see the thoughts behind them? thanks in
> > advance!
> Those values define the system attribute IDs associated to a relation.
> You can have a look at the top of heap.c to see where they come from,
> particularly the fields FormData_pg_attribute a1..a7.
> Hope this helps.
> Regards,
> --
> Michael
>