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
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.
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