Re: Re: parallel distinct union and aggregate support patch

> 1) It's better to always include the whole patch series - including the
> parts that have not changed. Otherwise people have to scavenge the
> thread and search for all the pieces, which may be a source of issues.
> Also, it confuses the patch tester [1] which tries to apply patches from
> a single message, so it will fail for this one.
Pathes 3 and 4 do not rely on 1 and 2 in code.
But, it will fail when you apply the apatches 3 and 4 directly, because
they are written after 1 and 2.
I can generate a new single patch if you need.

> 2) I suggest you try to describe the goal of these patches, using some
> example queries, explain output etc. Right now the reviewers have to
> reverse engineer the patches and deduce what the intention was, which
> may be causing unnecessary confusion etc. If this was my patch, I'd try
> to create a couple examples (CREATE TABLE + SELECT + EXPLAIN) showing
> how the patch changes the query plan, showing speedup etc.
I written some example queries in to regress, include "unique" "union"
"group by" and "group by grouping sets".
here is my tests, they are not in regress
```sql
begin;
create table gtest(id integer, txt text);
insert into gtest select t1.id,'txt'||t1.id from (select generate_series(1,1000*1000) id) t1,(select generate_series(1,10) id) t2;
analyze gtest;
commit;
set jit = off;
\timing on
```
normal aggregate times
```
set enable_batch_hashagg = off;
explain (costs off,analyze,verbose)
select sum(id),txt from gtest group by txt;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------
Finalize GroupAggregate (actual time=6469.279..8947.024 rows=1000000 loops=1)
Output: sum(id), txt
Group Key: gtest.txt
-> Gather Merge (actual time=6469.245..8165.930 rows=1000058 loops=1)
Output: txt, (PARTIAL sum(id))
Workers Planned: 2
Workers Launched: 2
-> Sort (actual time=6356.471..7133.832 rows=333353 loops=3)
Output: txt, (PARTIAL sum(id))
Sort Key: gtest.txt
Sort Method: external merge Disk: 11608kB
Worker 0: actual time=6447.665..7349.431 rows=317512 loops=1
Sort Method: external merge Disk: 10576kB
Worker 1: actual time=6302.882..7061.157 rows=333301 loops=1
Sort Method: external merge Disk: 11112kB
-> Partial HashAggregate (actual time=2591.487..4430.437 rows=333353 loops=3)
Output: txt, PARTIAL sum(id)
Group Key: gtest.txt
Batches: 17 Memory Usage: 4241kB Disk Usage: 113152kB
Worker 0: actual time=2584.345..4486.407 rows=317512 loops=1
Batches: 17 Memory Usage: 4241kB Disk Usage: 101392kB
Worker 1: actual time=2584.369..4393.244 rows=333301 loops=1
Batches: 17 Memory Usage: 4241kB Disk Usage: 112832kB
-> Parallel Seq Scan on public.gtest (actual time=0.691..603.990 rows=3333333 loops=3)
Output: id, txt
Worker 0: actual time=0.104..607.146 rows=3174970 loops=1
Worker 1: actual time=0.100..603.951 rows=3332785 loops=1
Planning Time: 0.226 ms
Execution Time: 9021.058 ms
(29 rows)

Time: 9022.251 ms (00:09.022)

set enable_batch_hashagg = on;
explain (costs off,analyze,verbose)
select sum(id),txt from gtest group by txt;
QUERY PLAN
-------------------------------------------------------------------------------------------------
Gather (actual time=3116.666..5740.826 rows=1000000 loops=1)
Output: (sum(id)), txt
Workers Planned: 2
Workers Launched: 2
-> Parallel BatchHashAggregate (actual time=3103.181..5464.948 rows=333333 loops=3)
Output: sum(id), txt
Group Key: gtest.txt
Worker 0: actual time=3094.550..5486.992 rows=326082 loops=1
Worker 1: actual time=3099.562..5480.111 rows=324729 loops=1
-> Parallel Seq Scan on public.gtest (actual time=0.791..656.601 rows=3333333 loops=3)
Output: id, txt
Worker 0: actual time=0.080..646.053 rows=3057680 loops=1
Worker 1: actual time=0.070..662.754 rows=3034370 loops=1
Planning Time: 0.243 ms
Execution Time: 5788.981 ms
(15 rows)

Time: 5790.143 ms (00:05.790)
```

grouping sets times
```
set enable_batch_hashagg = off;
explain (costs off,analyze,verbose)
select sum(id),txt from gtest group by grouping sets(id,txt,());
QUERY PLAN
------------------------------------------------------------------------------------------
GroupAggregate (actual time=9454.707..38921.885 rows=2000001 loops=1)
Output: sum(id), txt, id
Group Key: gtest.id
Group Key: ()
Sort Key: gtest.txt
Group Key: gtest.txt
-> Sort (actual time=9454.679..11804.071 rows=10000000 loops=1)
Output: txt, id
Sort Key: gtest.id
Sort Method: external merge Disk: 254056kB
-> Seq Scan on public.gtest (actual time=2.250..2419.031 rows=10000000 loops=1)
Output: txt, id
Planning Time: 0.230 ms
Execution Time: 39203.883 ms
(14 rows)

Time: 39205.339 ms (00:39.205)

set enable_batch_hashagg = on;
explain (costs off,analyze,verbose)
select sum(id),txt from gtest group by grouping sets(id,txt,());
QUERY PLAN
-------------------------------------------------------------------------------------------------
Gather (actual time=5931.776..14353.957 rows=2000001 loops=1)
Output: (sum(id)), txt, id
Workers Planned: 2
Workers Launched: 2
-> Parallel BatchHashAggregate (actual time=5920.963..13897.852 rows=666667 loops=3)
Output: sum(id), txt, id
Group Key: gtest.id
Group Key: ()
Group Key: gtest.txt
Worker 0: actual time=5916.370..14062.461 rows=513810 loops=1
Worker 1: actual time=5916.037..13932.847 rows=775901 loops=1
-> Parallel Seq Scan on public.gtest (actual time=0.399..688.273 rows=3333333 loops=3)
Output: id, txt
Worker 0: actual time=0.052..690.955 rows=3349990 loops=1
Worker 1: actual time=0.050..691.595 rows=3297070 loops=1
Planning Time: 0.157 ms
Execution Time: 14598.416 ms
(17 rows)

Time: 14599.437 ms (00:14.599)
```