Re: Push down more full joins in postgres_fdw

On Tue, Sep 27, 2016 at 8:48 AM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
> On 2016/09/26 20:20, Ashutosh Bapat wrote:
>>
>> On Mon, Sep 26, 2016 at 4:06 PM, Etsuro Fujita
>> <fujita.etsuro@lab.ntt.co.jp> wrote:
>>>
>>> On 2016/09/26 18:06, Ashutosh Bapat wrote:
>>>>
>>>> On Mon, Sep 26, 2016 at 1:05 PM, Etsuro Fujita
>>>> <fujita.etsuro@lab.ntt.co.jp> wrote:
>
>
>>>>> ISTM that the use of the same RTI for subqueries in multi-levels in a
>>>>> remote
>>>>> SQL makes the SQL a bit difficult to read.  How about using the
>>>>> position
>>>>> of
>>>>> the join rel in join_rel_list, (more precisely, the position plus
>>>>> list_length(root->parse->rtable)), instead?
>
>
>>>> We switch to hash table to maintain the join RelOptInfos when the
>>>> number of joins grows larger, where the position won't make much
>>>> sense.
>
>
>>> That's right, but we still store the joinrel into join_rel_list after
>>> creating that hash table.
>
>
>> As the list grows, it will take
>> longer to locate the RelOptInfo of the given join. Doing that for
>> creating an alias seems an overkill.
>
>
> The join rel is appended to the end of the list, so I was thinking to get
> the position info by list_length during postgresGetForeignJoinPaths.

That's true only when the paths are being added to a newly created
joinrel. But that's not true always. We may add paths with different
joining order to an existing joinrel, in which case list_length would
not give its position. Am I missing something?

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company