-- partitioned table: two partitions, each containing a t-digest with vastly
-- different compression values
CREATE TABLE digest_combine_test(k int, d tdigest) PARTITION BY LIST (k);
CREATE TABLE digest_combine_test_1 PARTITION OF digest_combine_test FOR VALUES IN (1);
CREATE TABLE digest_combine_test_2 PARTITION OF digest_combine_test FOR VALUES IN (2);
-- comp=10: BUFFER_SIZE=100 slots
INSERT INTO digest_combine_test SELECT 1, tdigest(v::float8, 10) FROM generate_series(1,100) v;
-- comp=10000: BUFFER_SIZE=10000 slots
INSERT INTO digest_combine_test SELECT 2, tdigest(v::float8, 10000) FROM generate_series(1,10000) v;
-- enough data to reliably trigger partitionwise aggregate
INSERT INTO digest_combine_test SELECT * FROM digest_combine_test;
INSERT INTO digest_combine_test SELECT * FROM digest_combine_test;
INSERT INTO digest_combine_test SELECT * FROM digest_combine_test;
ANALYZE digest_combine_test;
-- force partitionwise parallel aggregate
SET enable_partitionwise_aggregate = on;
SET max_parallel_workers_per_gather = 2;
SET parallel_leader_participation = off;
SET parallel_setup_cost = 0;
SET parallel_tuple_cost = 0;
SET min_parallel_table_scan_size = 0;
-- tdigest_combine(small, huge)
EXPLAIN (COSTS OFF)
SELECT tdigest(d) FROM digest_combine_test;
                        QUERY PLAN                         
-----------------------------------------------------------
 Finalize Aggregate
   ->  Gather
         Workers Planned: 2
         ->  Parallel Append
               ->  Partial Aggregate
                     ->  Seq Scan on digest_combine_test_1
               ->  Partial Aggregate
                     ->  Seq Scan on digest_combine_test_2
(8 rows)

SELECT tdigest(d) FROM digest_combine_test;
                                                                                                                                                           tdigest                                                                                                                                                           
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 flags 1 count 80800 compression 10 centroids 15 (1.000000, 1) (1.000000, 1) (1.000000, 8) (7.514286, 70) (72.955357, 560) (553.198115, 4457) (2362.044921, 19345) (5389.714865, 40465) (7942.990790, 10532) (9201.278639, 3937) (9702.287749, 1053) (9928.826923, 312) (9990.647059, 51) (9999.285714, 7) (10000.000000, 1)
(1 row)

DROP TABLE digest_combine_test;