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

2015-05-09 8:32 GMT+09:00 Kohei KaiGai <kaigai(at)kaigai(dot)gr(dot)jp>:
> 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);
>
The attached patch newly defines ExtraJoinPathArgs struct to pack
all the necessary information to be delivered on GetForeignJoinPaths
and set_join_pathlist_hook.

Its definition is below:
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;
} ExtraJoinPathArgs;

then, hook invocation gets much simplified, like:

/*
* 6. Finally, give extensions a chance to manipulate the path list.
*/
if (set_join_pathlist_hook)
set_join_pathlist_hook(&jargs);

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