spark-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From John Zhuge <jzh...@apache.org>
Subject Re: Why hint does not traverse down subquery alias
Date Wed, 12 Jun 2019 00:54:03 GMT
Yeah, it is a touch scenario.

I actually have much simpler cases:

1) select /*+ broadcast(t1) */ * from db.t1 join db.t2 on t1.id = t2.id;
2) select /*+ broadcast(t1) */ * from db.t1 a1 join db.t2 a2 on a1.id =
a2.id;

2) is the same as 1) but with aliases. Many users were surprised that 2)
stopped working.

Thanks,
John


On Tue, Jun 11, 2019 at 4:38 PM Maryann Xue <maryannxue@apache.org> wrote:

> Yes, and for a good reason: the hint relation has exactly the same scope
> with other elements of queries/sub-queries.
>
> Suppose there's a query like:
>
> select /*+ broadcast(s) */ from (select a, b from s) t join (select a, b
> from t) s on t1.a = t2.b
>
> If we allowed the hint resolving to "cross" the scopes, we'd end up with a
> really confusing spec.
>
>
> Thanks,
> Maryann
>
> On Tue, Jun 11, 2019 at 5:26 PM John Zhuge <jzhuge@apache.org> wrote:
>
>> Hi Reynold and Maryann,
>>
>> ResolveHints javadoc indicates the traversal does not go past subquery
>> alias. Is there any specific reason?
>>
>> Thanks,
>> John Zhuge
>>
>

-- 
John Zhuge

Mime
View raw message