Re: Custom/Foreign-Join-APIs (Re: [v9.5] Custom Plan API)

2015-05-09 3:51 GMT+09:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Fri, May 8, 2015 at 1:46 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> That's nice, but 9.5 feature freeze is only a week away. I don't have a
>>> lot of confidence that this stuff is actually in a state where we won't
>>> regret shipping it in 9.5.
>
>> Yeah. The POC you were asking for upthread certainly exists and has
>> for a while, or I would not have committed this. But I do not think
>> it likely that the postgres_fdw support will be ready for 9.5.
>
> Well, we have two alternatives. I can keep hacking on this and get it
> to a state where it seems credible to me, but we won't have any proof
> that it actually works (though perhaps we could treat any problems
> as bugs that should hopefully get found before 9.5 ships, if a
> postgres_fdw patch shows up in the next few months). Or we could
> revert the whole thing and bounce it to the 9.6 cycle. I don't really
> like doing the latter, but I'm pretty uncomfortable with committing to
> published FDW APIs that are (a) as messy as this and (b) practically
> untested. The odds that something slipped through the cracks are high.
>
> Aside from the other gripes I raised, I'm exceedingly unhappy with the
> ad-hoc APIs proposed for GetForeignJoinPaths and set_join_pathlist_hook.
> It's okay for internal calls in joinpath.c to look like that, but
> exporting that set of parameters seems like pure folly. We've changed
> those parameter lists repeatedly (for instance in 9.2 and again in 9.3);
> the odds that they'll need to change again in future approach 100%.
>
> One way we could reduce the risk of code breakage there is to stuff all
> or most of those parameters into a struct. This might result in a small
> slowdown for the internal calls, or then again maybe not --- there
> probably aren't many architectures that can pass 10 parameters in
> registers anyway.
>
Is it like a following structure definition?

typedef struct
{
PlannerInfo *root;
RelOptInfo *joinrel;
RelOptInfo *outerrel;
RelOptInfo *innerrel;
List *restrictlist;
JoinType jointype;
SpecialJoinInfo *sjinfo;
SemiAntiJoinFactors *semifactors;
Relids param_source_rels;
Relids extra_lateral_rels;
} SetJoinPathListArgs;

I agree the idea. It also helps CSP driver implementation where it calls
next driver that was already chained on its installation.

if (set_join_pathlist_next)
set_join_pathlist_next(args);

is more stable manner than

if (set_join_pathlist_next)
set_join_pathlist_next(root,
joinrel,
outerrel,
innerrel,
restrictlist,
jointype,
sjinfo,
semifactors,
param_source_rels,
extra_lateral_rels);

Thanks,
--
KaiGai Kohei <kaigai(at)kaigai(dot)gr(dot)jp>