Re: Keep notnullattrs in RelOptInfo (Was part of UniqueKey patch series)

>
> I assume we want to know if a Var is nullable with a function like.
> is_var_notnullable(Var *var, Relids relids). If so, we can define the
> data as below:
>
> struct RelOptInfo {
>
> Bitmapset** notnullattrs;
> ..
> };
>
> After this we can implement the function as:
>
> bool
> is_var_notnullable(Var* var, Relids relids)
> {
> RelOptInfo *rel = find_rel_by_relids(reldis);
> return bms_is_member(var->varattno, rel->notnullattrs[var->varno]);
> }
>
> Probably we can make some hackers to reduce the notnullattrs's memory usage
> overhead.
>
>
To be more precise, to make the rel->notnullattrs shorter, we can do the
following methods:
1). Relids only has single element, we can always use a 1-len array rather
than rel->varno
elements. 2). For multi-elements relids, we use the max(varno) as the
length of rel->notnullattrs.
3). For some cases, the notnullattrs of a baserel is not changed in later
stages, we can just
reuse the same Bitmapset * in later stages.

--
Best Regards
Andy Fan (https://www.aliyun.com/)