Re: asynchronous execution

On 2017/03/14 6:31, Corey Huinker wrote:
> On Mon, Mar 13, 2017 at 1:06 AM, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
> wrote:
>
>>
>>> I think it will, because Append itself has been made async-capable by one
>>> of the patches and UNION ALL uses Append. But as mentioned above, only
>>> the postgres_fdw foreign tables will be able to utilize this for now.
>>>
>>>
>> Ok, I'll re-run my test from a few weeks back and see if anything has
>> changed.
>>
>
>
> I'm not able to discern any difference in plan between a 9.6 instance and
> this patch.
>
> The basic outline of my test is:
>
> EXPLAIN ANALYZE
> SELECT c1, c2, ..., cN FROM tab1 WHERE date = '1 day ago'
> UNION ALL
> SELECT c1, c2, ..., cN FROM tab2 WHERE date = '2 days ago'
> UNION ALL
> SELECT c1, c2, ..., cN FROM tab3 WHERE date = '3 days ago'
> UNION ALL
> SELECT c1, c2, ..., cN FROM tab4 WHERE date = '4 days ago'
>
>
> I've tried this test where tab1 through tab4 all are the same postgres_fdw
> foreign table.
> I've tried this test where tab1 through tab4 all are different foreign
> tables pointing to the same remote table sharing a the same server
> definition.
> I've tried this test where tab1 through tab4 all are different foreign
> tables pointing each with it's own foreign server definition, all of which
> happen to point to the same remote cluster.
>
> Are there some postgresql.conf settings I should set to get a decent test?

I don't think the plan itself will change as a result of applying this
patch. You might however be able to observe some performance improvement.

Thanks,
Amit