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.paqu...@gmail.com>: > On Mon, Aug 18, 2014 at 4:42 PM, 土卜皿 <pengcz.n...@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 >
