how to understand these macro defines such as ObjectIdAttributeNumber in sysattr.h?
hi, all
I am so sorry for asking some questions like this!
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!
On Mon, Aug 18, 2014 at 4:42 PM, 土卜皿 <pengcz.nwpu@gmail.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
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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>:
Show quoted text
On Mon, Aug 18, 2014 at 4:42 PM, 土卜皿 <pengcz.nwpu@gmail.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
=?UTF-8?B?5Zyf5Y2c55q/?= <pengcz.nwpu@gmail.com> writes:
where and when using these system attributes?
http://www.postgresql.org/docs/devel/static/ddl-system-columns.html
regards, tom lane
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