Partitions aggregation

[Krysztophe]

We have more an d more plans with many partitions that make unreadable plans

I'd like pev2 to « aggregate » the nodes of the partitions.
Of course, all partitions do not have the same plans.

I'm note sure that detecting the Append nodes should be enough.

Te user should be alble to partition this « partition aware » mode with a checkbox.

Some simple use cases:

--  pgbench -i -s 100 --partitions=100 
SET max_parallel_workers_per_gather TO 0 ;

-- https://explain.dalibo.com/plan/gggcb54d3a04d505
EXPLAIN (ANALYZE,BUFFERS,VERBOSE)
SELECT * FROM pgbench_accounts
WHERE aid +0  = 888 ;

-- https://explain.dalibo.com/plan/3179a1834085acg1
EXPLAIN (ANALYZE,BUFFERS)
SELECT SUM(aid) FROM pgbench_accounts
WHERE aid +0  = 888 ;

--- With  VERBOSE :
-- https://explain.dalibo.com/plan/4b8e8d1bhg565gc5 


SET max_parallel_workers_per_gather TO 2 ;

-- https://explain.dalibo.com/plan/acb7c49587899129
EXPLAIN (ANALYZE,BUFFERS,VERBOSE)
SELECT * FROM pgbench_accounts
WHERE aid +0  = 888 ;

---- To have different plans on the partitions
CREATE INDEX ON pgbench_accounts_6 ((aid+0)) ;
CREATE INDEX ON pgbench_accounts_8 ((aid+0)) ;

SET max_parallel_workers_per_gather TO 0 ;

-- https://explain.dalibo.com/plan/9eb585d3ch3914g1
EXPLAIN (ANALYZE,BUFFERS,VERBOSE)
SELECT * FROM pgbench_accounts
WHERE aid +0  = 888 ;

VACUUM ANALYZE ;

-- https://explain.dalibo.com/plan/0ha3gedh3h21761f
EXPLAIN (ANALYZE,BUFFERS,VERBOSE)

SELECT * FROM pgbench_accounts
WHERE aid +0  = 888 ;

-- https://explain.dalibo.com/plan/g6f2ga726c9d38cf
SET max_parallel_workers_per_gather TO 0 ;
EXPLAIN (ANALYZE,BUFFERS)
SELECT SUM(aid) FROM pgbench_accounts
WHERE aid +0  = 888 ;