postgresql/src/test/regress/expected/incremental_sort.out

-- When we have to sort the entire table, incremental sort will
-- be slower than plain sort, so it should not be used.
explain (costs off)
select * from (select * from tenk1 order by four) t order by four, ten;
            QUERY PLAN             
-----------------------------------
 Sort
   Sort Key: tenk1.four, tenk1.ten
   ->  Sort
         Sort Key: tenk1.four
         ->  Seq Scan on tenk1
(5 rows)

-- When there is a LIMIT clause, incremental sort is beneficial because
-- it only has to sort some of the groups, and not the entire table.
explain (costs off)
select * from (select * from tenk1 order by four) t order by four, ten
limit 1;
               QUERY PLAN                
-----------------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: tenk1.four, tenk1.ten
         Presorted Key: tenk1.four
         ->  Sort
               Sort Key: tenk1.four
               ->  Seq Scan on tenk1
(7 rows)

-- When work_mem is not enough to sort the entire table, incremental sort
-- may be faster if individual groups still fit into work_mem.
set work_mem to '2MB';
explain (costs off)
select * from (select * from tenk1 order by four) t order by four, ten;
            QUERY PLAN             
-----------------------------------
 Incremental Sort
   Sort Key: tenk1.four, tenk1.ten
   Presorted Key: tenk1.four
   ->  Sort
         Sort Key: tenk1.four
         ->  Seq Scan on tenk1
(6 rows)

reset work_mem;
create table t(a integer, b integer);
create or replace function explain_analyze_without_memory(query text)
returns table (out_line text) language plpgsql
as
$$
declare
  line text;
begin
  for line in
    execute 'explain (analyze, costs off, summary off, timing off) ' || query
  loop
    out_line := regexp_replace(line, '\d+kB', 'NNkB', 'g');
    return next;
  end loop;
end;
$$;
create or replace function explain_analyze_inc_sort_nodes(query text)
returns jsonb language plpgsql
as
$$
declare
  elements jsonb;
  element jsonb;
  matching_nodes jsonb := '[]'::jsonb;
begin
  execute 'explain (analyze, costs off, summary off, timing off, format ''json'') ' || query into strict elements;
  while jsonb_array_length(elements) > 0 loop
    element := elements->0;
    elements := elements - 0;
    case jsonb_typeof(element)
    when 'array' then
      if jsonb_array_length(element) > 0 then
        elements := elements || element;
      end if;
    when 'object' then
      if element ? 'Plan' then
        elements := elements || jsonb_build_array(element->'Plan');
        element := element - 'Plan';
      else
        if element ? 'Plans' then
          elements := elements || jsonb_build_array(element->'Plans');
          element := element - 'Plans';
        end if;
        if (element->>'Node Type')::text = 'Incremental Sort' then
          matching_nodes := matching_nodes || element;
        end if;
      end if;
    end case;
  end loop;
  return matching_nodes;
end;
$$;
create or replace function explain_analyze_inc_sort_nodes_without_memory(query text)
returns jsonb language plpgsql
as
$$
declare
  nodes jsonb := '[]'::jsonb;
  node jsonb;
  group_key text;
  space_key text;
begin
  for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
    for group_key in select unnest(array['Full-sort Groups', 'Presorted Groups']::text[]) t loop
      for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
        node := jsonb_set(node, array[group_key, space_key, 'Average Sort Space Used'], '"NN"', false);
        node := jsonb_set(node, array[group_key, space_key, 'Peak Sort Space Used'], '"NN"', false);
      end loop;
    end loop;
    nodes := nodes || node;
  end loop;
  return nodes;
end;
$$;
create or replace function explain_analyze_inc_sort_nodes_verify_invariants(query text)
returns bool language plpgsql
as
$$
declare
  node jsonb;
  group_stats jsonb;
  group_key text;
  space_key text;
begin
  for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
    for group_key in select unnest(array['Full-sort Groups', 'Presorted Groups']::text[]) t loop
      group_stats := node->group_key;
      for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
        if (group_stats->space_key->'Peak Sort Space Used')::bigint < (group_stats->space_key->'Peak Sort Space Used')::bigint then
          raise exception '% has invalid max space < average space', group_key;
        end if;
      end loop;
    end loop;
  end loop;
  return true;
end;
$$;
-- A single large group tested around each mode transition point.
insert into t(a, b) select i/100 + 1, i + 1 from generate_series(0, 999) n(i);
analyze t;
explain (costs off) select * from (select * from t order by a) s order by a, b limit 31;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 31;
 a | b  
---+----
 1 |  1
 1 |  2
 1 |  3
 1 |  4
 1 |  5
 1 |  6
 1 |  7
 1 |  8
 1 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 1 | 20
 1 | 21
 1 | 22
 1 | 23
 1 | 24
 1 | 25
 1 | 26
 1 | 27
 1 | 28
 1 | 29
 1 | 30
 1 | 31
(31 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 32;
 a | b  
---+----
 1 |  1
 1 |  2
 1 |  3
 1 |  4
 1 |  5
 1 |  6
 1 |  7
 1 |  8
 1 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 1 | 20
 1 | 21
 1 | 22
 1 | 23
 1 | 24
 1 | 25
 1 | 26
 1 | 27
 1 | 28
 1 | 29
 1 | 30
 1 | 31
 1 | 32
(32 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 33;
 a | b  
---+----
 1 |  1
 1 |  2
 1 |  3
 1 |  4
 1 |  5
 1 |  6
 1 |  7
 1 |  8
 1 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 1 | 20
 1 | 21
 1 | 22
 1 | 23
 1 | 24
 1 | 25
 1 | 26
 1 | 27
 1 | 28
 1 | 29
 1 | 30
 1 | 31
 1 | 32
 1 | 33
(33 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 65;
 a | b  
---+----
 1 |  1
 1 |  2
 1 |  3
 1 |  4
 1 |  5
 1 |  6
 1 |  7
 1 |  8
 1 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 1 | 20
 1 | 21
 1 | 22
 1 | 23
 1 | 24
 1 | 25
 1 | 26
 1 | 27
 1 | 28
 1 | 29
 1 | 30
 1 | 31
 1 | 32
 1 | 33
 1 | 34
 1 | 35
 1 | 36
 1 | 37
 1 | 38
 1 | 39
 1 | 40
 1 | 41
 1 | 42
 1 | 43
 1 | 44
 1 | 45
 1 | 46
 1 | 47
 1 | 48
 1 | 49
 1 | 50
 1 | 51
 1 | 52
 1 | 53
 1 | 54
 1 | 55
 1 | 56
 1 | 57
 1 | 58
 1 | 59
 1 | 60
 1 | 61
 1 | 62
 1 | 63
 1 | 64
 1 | 65
(65 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 66;
 a | b  
---+----
 1 |  1
 1 |  2
 1 |  3
 1 |  4
 1 |  5
 1 |  6
 1 |  7
 1 |  8
 1 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 1 | 20
 1 | 21
 1 | 22
 1 | 23
 1 | 24
 1 | 25
 1 | 26
 1 | 27
 1 | 28
 1 | 29
 1 | 30
 1 | 31
 1 | 32
 1 | 33
 1 | 34
 1 | 35
 1 | 36
 1 | 37
 1 | 38
 1 | 39
 1 | 40
 1 | 41
 1 | 42
 1 | 43
 1 | 44
 1 | 45
 1 | 46
 1 | 47
 1 | 48
 1 | 49
 1 | 50
 1 | 51
 1 | 52
 1 | 53
 1 | 54
 1 | 55
 1 | 56
 1 | 57
 1 | 58
 1 | 59
 1 | 60
 1 | 61
 1 | 62
 1 | 63
 1 | 64
 1 | 65
 1 | 66
(66 rows)

delete from t;
-- An initial large group followed by a small group.
insert into t(a, b) select i/50 + 1, i + 1 from generate_series(0, 999) n(i);
analyze t;
explain (costs off) select * from (select * from t order by a) s order by a, b limit 55;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 55;
 a | b  
---+----
 1 |  1
 1 |  2
 1 |  3
 1 |  4
 1 |  5
 1 |  6
 1 |  7
 1 |  8
 1 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 1 | 20
 1 | 21
 1 | 22
 1 | 23
 1 | 24
 1 | 25
 1 | 26
 1 | 27
 1 | 28
 1 | 29
 1 | 30
 1 | 31
 1 | 32
 1 | 33
 1 | 34
 1 | 35
 1 | 36
 1 | 37
 1 | 38
 1 | 39
 1 | 40
 1 | 41
 1 | 42
 1 | 43
 1 | 44
 1 | 45
 1 | 46
 1 | 47
 1 | 48
 1 | 49
 1 | 50
 2 | 51
 2 | 52
 2 | 53
 2 | 54
 2 | 55
(55 rows)

-- Test EXPLAIN ANALYZE with only a fullsort group.
select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 55');
                                 explain_analyze_without_memory                                 
------------------------------------------------------------------------------------------------
 Limit (actual rows=55 loops=1)
   ->  Incremental Sort (actual rows=55 loops=1)
         Sort Key: t.a, t.b
         Presorted Key: t.a
         Full-sort Groups: 2 Sort Methods: top-N heapsort, quicksort Memory: avg=NNkB peak=NNkB
         ->  Sort (actual rows=101 loops=1)
               Sort Key: t.a
               Sort Method: quicksort  Memory: NNkB
               ->  Seq Scan on t (actual rows=1000 loops=1)
(9 rows)

select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 55'));
                  jsonb_pretty                   
-------------------------------------------------
 [                                              +
     {                                          +
         "Sort Key": [                          +
             "t.a",                             +
             "t.b"                              +
         ],                                     +
         "Node Type": "Incremental Sort",       +
         "Actual Rows": 55,                     +
         "Actual Loops": 1,                     +
         "Presorted Key": [                     +
             "t.a"                              +
         ],                                     +
         "Parallel Aware": false,               +
         "Full-sort Groups": {                  +
             "Group Count": 2,                  +
             "Sort Methods Used": [             +
                 "top-N heapsort",              +
                 "quicksort"                    +
             ],                                 +
             "Sort Space Memory": {             +
                 "Peak Sort Space Used": "NN",  +
                 "Average Sort Space Used": "NN"+
             }                                  +
         },                                     +
         "Parent Relationship": "Outer"         +
     }                                          +
 ]
(1 row)

select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 55');
 explain_analyze_inc_sort_nodes_verify_invariants 
--------------------------------------------------
 t
(1 row)

delete from t;
-- An initial small group followed by a large group.
insert into t(a, b) select (case when i < 5 then i else 9 end), i from generate_series(1, 1000) n(i);
analyze t;
explain (costs off) select * from (select * from t order by a) s order by a, b limit 70;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 70;
 a | b  
---+----
 1 |  1
 2 |  2
 3 |  3
 4 |  4
 9 |  5
 9 |  6
 9 |  7
 9 |  8
 9 |  9
 9 | 10
 9 | 11
 9 | 12
 9 | 13
 9 | 14
 9 | 15
 9 | 16
 9 | 17
 9 | 18
 9 | 19
 9 | 20
 9 | 21
 9 | 22
 9 | 23
 9 | 24
 9 | 25
 9 | 26
 9 | 27
 9 | 28
 9 | 29
 9 | 30
 9 | 31
 9 | 32
 9 | 33
 9 | 34
 9 | 35
 9 | 36
 9 | 37
 9 | 38
 9 | 39
 9 | 40
 9 | 41
 9 | 42
 9 | 43
 9 | 44
 9 | 45
 9 | 46
 9 | 47
 9 | 48
 9 | 49
 9 | 50
 9 | 51
 9 | 52
 9 | 53
 9 | 54
 9 | 55
 9 | 56
 9 | 57
 9 | 58
 9 | 59
 9 | 60
 9 | 61
 9 | 62
 9 | 63
 9 | 64
 9 | 65
 9 | 66
 9 | 67
 9 | 68
 9 | 69
 9 | 70
(70 rows)

-- Test rescan.
begin;
-- We force the planner to choose a plan with incremental sort on the right side
-- of a nested loop join node. That way we trigger the rescan code path.
set local enable_hashjoin = off;
set local enable_mergejoin = off;
set local enable_material = off;
set local enable_sort = off;
explain (costs off) select * from t left join (select * from (select * from t order by a) v order by a, b) s on s.a = t.a where t.a in (1, 2);
                   QUERY PLAN                   
------------------------------------------------
 Nested Loop Left Join
   Join Filter: (t_1.a = t.a)
   ->  Seq Scan on t
         Filter: (a = ANY ('{1,2}'::integer[]))
   ->  Incremental Sort
         Sort Key: t_1.a, t_1.b
         Presorted Key: t_1.a
         ->  Sort
               Sort Key: t_1.a
               ->  Seq Scan on t t_1
(10 rows)

select * from t left join (select * from (select * from t order by a) v order by a, b) s on s.a = t.a where t.a in (1, 2);
 a | b | a | b 
---+---+---+---
 1 | 1 | 1 | 1
 2 | 2 | 2 | 2
(2 rows)

rollback;
-- Test EXPLAIN ANALYZE with both fullsort and presorted groups.
select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 70');
                                                                    explain_analyze_without_memory                                                                    
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit (actual rows=70 loops=1)
   ->  Incremental Sort (actual rows=70 loops=1)
         Sort Key: t.a, t.b
         Presorted Key: t.a
         Full-sort Groups: 1 Sort Method: quicksort Memory: avg=NNkB peak=NNkB Presorted Groups: 5 Sort Methods: top-N heapsort, quicksort Memory: avg=NNkB peak=NNkB
         ->  Sort (actual rows=1000 loops=1)
               Sort Key: t.a
               Sort Method: quicksort  Memory: NNkB
               ->  Seq Scan on t (actual rows=1000 loops=1)
(9 rows)

select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 70'));
                  jsonb_pretty                   
-------------------------------------------------
 [                                              +
     {                                          +
         "Sort Key": [                          +
             "t.a",                             +
             "t.b"                              +
         ],                                     +
         "Node Type": "Incremental Sort",       +
         "Actual Rows": 70,                     +
         "Actual Loops": 1,                     +
         "Presorted Key": [                     +
             "t.a"                              +
         ],                                     +
         "Parallel Aware": false,               +
         "Full-sort Groups": {                  +
             "Group Count": 1,                  +
             "Sort Methods Used": [             +
                 "quicksort"                    +
             ],                                 +
             "Sort Space Memory": {             +
                 "Peak Sort Space Used": "NN",  +
                 "Average Sort Space Used": "NN"+
             }                                  +
         },                                     +
         "Presorted Groups": {                  +
             "Group Count": 5,                  +
             "Sort Methods Used": [             +
                 "top-N heapsort",              +
                 "quicksort"                    +
             ],                                 +
             "Sort Space Memory": {             +
                 "Peak Sort Space Used": "NN",  +
                 "Average Sort Space Used": "NN"+
             }                                  +
         },                                     +
         "Parent Relationship": "Outer"         +
     }                                          +
 ]
(1 row)

select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 70');
 explain_analyze_inc_sort_nodes_verify_invariants 
--------------------------------------------------
 t
(1 row)

delete from t;
-- Small groups of 10 tuples each tested around each mode transition point.
insert into t(a, b) select i / 10, i from generate_series(1, 1000) n(i);
analyze t;
explain (costs off) select * from (select * from t order by a) s order by a, b limit 31;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 31;
 a | b  
---+----
 0 |  1
 0 |  2
 0 |  3
 0 |  4
 0 |  5
 0 |  6
 0 |  7
 0 |  8
 0 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 2 | 20
 2 | 21
 2 | 22
 2 | 23
 2 | 24
 2 | 25
 2 | 26
 2 | 27
 2 | 28
 2 | 29
 3 | 30
 3 | 31
(31 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 32;
 a | b  
---+----
 0 |  1
 0 |  2
 0 |  3
 0 |  4
 0 |  5
 0 |  6
 0 |  7
 0 |  8
 0 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 2 | 20
 2 | 21
 2 | 22
 2 | 23
 2 | 24
 2 | 25
 2 | 26
 2 | 27
 2 | 28
 2 | 29
 3 | 30
 3 | 31
 3 | 32
(32 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 33;
 a | b  
---+----
 0 |  1
 0 |  2
 0 |  3
 0 |  4
 0 |  5
 0 |  6
 0 |  7
 0 |  8
 0 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 2 | 20
 2 | 21
 2 | 22
 2 | 23
 2 | 24
 2 | 25
 2 | 26
 2 | 27
 2 | 28
 2 | 29
 3 | 30
 3 | 31
 3 | 32
 3 | 33
(33 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 65;
 a | b  
---+----
 0 |  1
 0 |  2
 0 |  3
 0 |  4
 0 |  5
 0 |  6
 0 |  7
 0 |  8
 0 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 2 | 20
 2 | 21
 2 | 22
 2 | 23
 2 | 24
 2 | 25
 2 | 26
 2 | 27
 2 | 28
 2 | 29
 3 | 30
 3 | 31
 3 | 32
 3 | 33
 3 | 34
 3 | 35
 3 | 36
 3 | 37
 3 | 38
 3 | 39
 4 | 40
 4 | 41
 4 | 42
 4 | 43
 4 | 44
 4 | 45
 4 | 46
 4 | 47
 4 | 48
 4 | 49
 5 | 50
 5 | 51
 5 | 52
 5 | 53
 5 | 54
 5 | 55
 5 | 56
 5 | 57
 5 | 58
 5 | 59
 6 | 60
 6 | 61
 6 | 62
 6 | 63
 6 | 64
 6 | 65
(65 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 66;
 a | b  
---+----
 0 |  1
 0 |  2
 0 |  3
 0 |  4
 0 |  5
 0 |  6
 0 |  7
 0 |  8
 0 |  9
 1 | 10
 1 | 11
 1 | 12
 1 | 13
 1 | 14
 1 | 15
 1 | 16
 1 | 17
 1 | 18
 1 | 19
 2 | 20
 2 | 21
 2 | 22
 2 | 23
 2 | 24
 2 | 25
 2 | 26
 2 | 27
 2 | 28
 2 | 29
 3 | 30
 3 | 31
 3 | 32
 3 | 33
 3 | 34
 3 | 35
 3 | 36
 3 | 37
 3 | 38
 3 | 39
 4 | 40
 4 | 41
 4 | 42
 4 | 43
 4 | 44
 4 | 45
 4 | 46
 4 | 47
 4 | 48
 4 | 49
 5 | 50
 5 | 51
 5 | 52
 5 | 53
 5 | 54
 5 | 55
 5 | 56
 5 | 57
 5 | 58
 5 | 59
 6 | 60
 6 | 61
 6 | 62
 6 | 63
 6 | 64
 6 | 65
 6 | 66
(66 rows)

delete from t;
-- Small groups of only 1 tuple each tested around each mode transition point.
insert into t(a, b) select i, i from generate_series(1, 1000) n(i);
analyze t;
explain (costs off) select * from (select * from t order by a) s order by a, b limit 31;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 31;
 a  | b  
----+----
  1 |  1
  2 |  2
  3 |  3
  4 |  4
  5 |  5
  6 |  6
  7 |  7
  8 |  8
  9 |  9
 10 | 10
 11 | 11
 12 | 12
 13 | 13
 14 | 14
 15 | 15
 16 | 16
 17 | 17
 18 | 18
 19 | 19
 20 | 20
 21 | 21
 22 | 22
 23 | 23
 24 | 24
 25 | 25
 26 | 26
 27 | 27
 28 | 28
 29 | 29
 30 | 30
 31 | 31
(31 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 32;
 a  | b  
----+----
  1 |  1
  2 |  2
  3 |  3
  4 |  4
  5 |  5
  6 |  6
  7 |  7
  8 |  8
  9 |  9
 10 | 10
 11 | 11
 12 | 12
 13 | 13
 14 | 14
 15 | 15
 16 | 16
 17 | 17
 18 | 18
 19 | 19
 20 | 20
 21 | 21
 22 | 22
 23 | 23
 24 | 24
 25 | 25
 26 | 26
 27 | 27
 28 | 28
 29 | 29
 30 | 30
 31 | 31
 32 | 32
(32 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 33;
 a  | b  
----+----
  1 |  1
  2 |  2
  3 |  3
  4 |  4
  5 |  5
  6 |  6
  7 |  7
  8 |  8
  9 |  9
 10 | 10
 11 | 11
 12 | 12
 13 | 13
 14 | 14
 15 | 15
 16 | 16
 17 | 17
 18 | 18
 19 | 19
 20 | 20
 21 | 21
 22 | 22
 23 | 23
 24 | 24
 25 | 25
 26 | 26
 27 | 27
 28 | 28
 29 | 29
 30 | 30
 31 | 31
 32 | 32
 33 | 33
(33 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 65;
 a  | b  
----+----
  1 |  1
  2 |  2
  3 |  3
  4 |  4
  5 |  5
  6 |  6
  7 |  7
  8 |  8
  9 |  9
 10 | 10
 11 | 11
 12 | 12
 13 | 13
 14 | 14
 15 | 15
 16 | 16
 17 | 17
 18 | 18
 19 | 19
 20 | 20
 21 | 21
 22 | 22
 23 | 23
 24 | 24
 25 | 25
 26 | 26
 27 | 27
 28 | 28
 29 | 29
 30 | 30
 31 | 31
 32 | 32
 33 | 33
 34 | 34
 35 | 35
 36 | 36
 37 | 37
 38 | 38
 39 | 39
 40 | 40
 41 | 41
 42 | 42
 43 | 43
 44 | 44
 45 | 45
 46 | 46
 47 | 47
 48 | 48
 49 | 49
 50 | 50
 51 | 51
 52 | 52
 53 | 53
 54 | 54
 55 | 55
 56 | 56
 57 | 57
 58 | 58
 59 | 59
 60 | 60
 61 | 61
 62 | 62
 63 | 63
 64 | 64
 65 | 65
(65 rows)

explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
           QUERY PLAN            
---------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: t.a, t.b
         Presorted Key: t.a
         ->  Sort
               Sort Key: t.a
               ->  Seq Scan on t
(7 rows)

select * from (select * from t order by a) s order by a, b limit 66;
 a  | b  
----+----
  1 |  1
  2 |  2
  3 |  3
  4 |  4
  5 |  5
  6 |  6
  7 |  7
  8 |  8
  9 |  9
 10 | 10
 11 | 11
 12 | 12
 13 | 13
 14 | 14
 15 | 15
 16 | 16
 17 | 17
 18 | 18
 19 | 19
 20 | 20
 21 | 21
 22 | 22
 23 | 23
 24 | 24
 25 | 25
 26 | 26
 27 | 27
 28 | 28
 29 | 29
 30 | 30
 31 | 31
 32 | 32
 33 | 33
 34 | 34
 35 | 35
 36 | 36
 37 | 37
 38 | 38
 39 | 39
 40 | 40
 41 | 41
 42 | 42
 43 | 43
 44 | 44
 45 | 45
 46 | 46
 47 | 47
 48 | 48
 49 | 49
 50 | 50
 51 | 51
 52 | 52
 53 | 53
 54 | 54
 55 | 55
 56 | 56
 57 | 57
 58 | 58
 59 | 59
 60 | 60
 61 | 61
 62 | 62
 63 | 63
 64 | 64
 65 | 65
 66 | 66
(66 rows)

delete from t;
drop table t;
-- Incremental sort vs. parallel queries
set min_parallel_table_scan_size = '1kB';
set min_parallel_index_scan_size = '1kB';
set parallel_setup_cost = 0;
set parallel_tuple_cost = 0;
set max_parallel_workers_per_gather = 2;
create table t (a int, b int, c int);
insert into t select mod(i,10),mod(i,10),i from generate_series(1,10000) s(i);
create index on t (a);
analyze t;
set enable_incrementalsort = off;
explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1;
                      QUERY PLAN                      
------------------------------------------------------
 Limit
   ->  Sort
         Sort Key: a, b, (sum(c))
         ->  Finalize HashAggregate
               Group Key: a, b
               ->  Gather
                     Workers Planned: 2
                     ->  Partial HashAggregate
                           Group Key: a, b
                           ->  Parallel Seq Scan on t
(10 rows)

set enable_incrementalsort = on;
explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1;
                              QUERY PLAN                              
----------------------------------------------------------------------
 Limit
   ->  Incremental Sort
         Sort Key: a, b, (sum(c))
         Presorted Key: a, b
         ->  GroupAggregate
               Group Key: a, b
               ->  Gather Merge
                     Workers Planned: 2
                     ->  Incremental Sort
                           Sort Key: a, b
                           Presorted Key: a
                           ->  Parallel Index Scan using t_a_idx on t
(12 rows)

-- Incremental sort vs. set operations with varno 0
set enable_hashagg to off;
explain (costs off) select * from t union select * from t order by 1,3;
                        QUERY PLAN                        
----------------------------------------------------------
 Incremental Sort
   Sort Key: t.a, t.c
   Presorted Key: t.a
   ->  Unique
         ->  Sort
               Sort Key: t.a, t.b, t.c
               ->  Append
                     ->  Gather
                           Workers Planned: 2
                           ->  Parallel Seq Scan on t
                     ->  Gather
                           Workers Planned: 2
                           ->  Parallel Seq Scan on t t_1
(13 rows)

drop table t;