Re: EXPLAIN VERBOSE with parallel Aggregate

On 27 April 2016 at 12:37, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Apr 26, 2016 at 6:44 PM, David Rowley
> <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>> On 27 April 2016 at 08:46, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>>> My proposed fix for this issue is attached. Review is welcome;
>>> otherwise, I'll just commit this. The output looks like what I
>>> suggested upthread:
>>
>> + if (!aggref->aggpartial)
>> + elog(ERROR, "referenced Aggref is not partial");
>>
>> I think this is overly restrictive; ruleutils seems a bit out of line
>> here to say that plans can't have > 1 combine aggregate node.
>>
>> When coding the combine aggs stuff I had test code to inject
>> additional combine paths to make sure everything worked as expected.
>> It did, but it won't if you add these two lines. I'd say just remove
>> them.
>>
>> If you apply the attached and execute;
>>
>> create table t1 (num int not null);
>> insert into t1 select generate_series(1,2000000);
>>
>> explain verbose select avg(num) from t1;
>>
>> You'll get;
>>
>> ERROR: referenced Aggref is not partial
>
> In this test patch, should aggpath be using partial_grouping_target
> rather than target? I feel like we need to use
> partial_grouping_target unless finalizeAggs is true.

Yes. I should also have removed the HAVING clause from the path.

After having changed that, I do still get the error.

I changed it to a NOTICE for now;

# explain verbose select avg(num) from t1 having sum(num) > 0;
NOTICE: referenced Aggref is not partial
NOTICE: referenced Aggref is not partial
QUERY PLAN
---------------------------------------------------------------------------------------------------
Finalize Aggregate (cost=22350.24..22350.25 rows=1 width=32)
Output: avg(num)
Filter: (sum(t1.num) > 0)
-> Partial Aggregate (cost=22350.22..22350.23 rows=1 width=40)
Output: avg(num), sum(num)
-> Gather (cost=22350.00..22350.21 rows=2 width=40)
Output: (PARTIAL avg(num)), (PARTIAL sum(num))
Workers Planned: 2
-> Partial Aggregate (cost=21350.00..21350.01 rows=1 width=40)
Output: PARTIAL avg(num), PARTIAL sum(num)
-> Parallel Seq Scan on public.t1
(cost=0.00..17183.33 rows=833333 width=4)
Output: num
(12 rows)

You can see that the middle aggregate node properly includes the
sum(num) from the having clause, so is using the partial target list.

I'd also have expected the output of both partial nodes to be the
same, i.e. both prefixed with PARTIAL. Is it intended that they don't?
or have I made some other mistake?

--
David Rowley http://www.2ndQuadrant.com/
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