Re: how to understand these macro defines such as ObjectIdAttributeNumber in sysattr.h?
| От | 土卜皿 |
|---|---|
| Тема | Re: how to understand these macro defines such as ObjectIdAttributeNumber in sysattr.h? |
| Дата | |
| Msg-id | CADT5_1-m3P_pf+OKYMNwb+yr2-Cw8v=iqYQRXizH=DN2MC64NA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: how to understand these macro defines such as ObjectIdAttributeNumber in sysattr.h? (Michael Paquier <michael.paquier@gmail.com>) |
| Ответы |
Re: how to understand these macro defines such as ObjectIdAttributeNumber in sysattr.h?
|
| Список | pgsql-hackers |
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.paquier@gmail.com>:
On Mon, Aug 18, 2014 at 4:42 PM, 土卜皿 <pengcz.nwpu@gmail.com> wrote:Those values define the system attribute IDs associated to a relation.
> 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!
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
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