mirror of
https://github.com/postgres/postgres.git
synced 2026-02-22 01:11:05 -05:00
80dc07aa36
The inner loop in switchToPresortedPrefixMode() can be implemented
as a conventional integer-counter for() loop, removing a couple of
redundant boolean state variables. The old logic here was a remnant
of earlier development, but as things now stand there's no reason
for extra complexity.
Also, annotate the test case added by 82e0e2930 to explain why it
manages to hit the corner case fixed in that commit, and add an
EXPLAIN to verify that it's creating an incremental-sort plan.
Back-patch to v13, like the previous patch.
James Coleman and Tom Lane
Discussion: https://postgr.es/m/16846-ae49f51ac379a4cb@postgresql.org
278 lines
12 KiB
PL/PgSQL
278 lines
12 KiB
PL/PgSQL
-- 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;
|
|
|
|
-- 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;
|
|
|
|
-- 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;
|
|
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
|
|
$$
|
|
declare
|
|
nodes jsonb := '[]'::jsonb;
|
|
node jsonb;
|
|
group_key text;
|
|
space_key text;
|
|
begin
|
|
for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
|
|
for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
|
|
for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
|
|
node := jsonb_set(node, array[group_key, space_key, 'Average Sort Space Used'], '"NN"', false);
|
|
node := jsonb_set(node, array[group_key, space_key, 'Peak Sort Space Used'], '"NN"', false);
|
|
end loop;
|
|
end loop;
|
|
nodes := nodes || node;
|
|
end loop;
|
|
return nodes;
|
|
end;
|
|
$$;
|
|
|
|
create or replace function explain_analyze_inc_sort_nodes_verify_invariants(query text)
|
|
returns bool language plpgsql
|
|
as
|
|
$$
|
|
declare
|
|
node jsonb;
|
|
group_stats jsonb;
|
|
group_key text;
|
|
space_key text;
|
|
begin
|
|
for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
|
|
for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
|
|
group_stats := node->group_key;
|
|
for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
|
|
if (group_stats->space_key->'Peak Sort Space Used')::bigint < (group_stats->space_key->'Peak Sort Space Used')::bigint then
|
|
raise exception '% has invalid max space < average space', group_key;
|
|
end if;
|
|
end loop;
|
|
end loop;
|
|
end loop;
|
|
return true;
|
|
end;
|
|
$$;
|
|
|
|
-- 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;
|
|
select * from (select * from t order by a) s order by a, b limit 31;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
|
|
select * from (select * from t order by a) s order by a, b limit 32;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
|
|
select * from (select * from t order by a) s order by a, b limit 33;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
|
|
select * from (select * from t order by a) s order by a, b limit 65;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
|
|
select * from (select * from t order by a) s order by a, b limit 66;
|
|
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;
|
|
select * from (select * from t order by a) s order by a, b limit 55;
|
|
-- 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');
|
|
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'));
|
|
select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 55');
|
|
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;
|
|
select * from (select * from t order by a) s order by a, b limit 70;
|
|
-- Checks case where we hit a group boundary at the last tuple of a batch.
|
|
-- Because the full sort state is bounded, we scan 64 tuples (the mode
|
|
-- transition point) but only retain 5. Thus when we transition modes, all
|
|
-- tuples in the full sort state have different prefix keys.
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 5;
|
|
select * from (select * from t order by a) s order by a, b limit 5;
|
|
|
|
-- 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);
|
|
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);
|
|
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');
|
|
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'));
|
|
select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 70');
|
|
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;
|
|
select * from (select * from t order by a) s order by a, b limit 31;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
|
|
select * from (select * from t order by a) s order by a, b limit 32;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
|
|
select * from (select * from t order by a) s order by a, b limit 33;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
|
|
select * from (select * from t order by a) s order by a, b limit 65;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
|
|
select * from (select * from t order by a) s order by a, b limit 66;
|
|
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;
|
|
select * from (select * from t order by a) s order by a, b limit 31;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
|
|
select * from (select * from t order by a) s order by a, b limit 32;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
|
|
select * from (select * from t order by a) s order by a, b limit 33;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
|
|
select * from (select * from t order by a) s order by a, b limit 65;
|
|
explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
|
|
select * from (select * from t order by a) s order by a, b limit 66;
|
|
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_incremental_sort = off;
|
|
explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1;
|
|
|
|
set enable_incremental_sort = on;
|
|
explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1;
|
|
|
|
-- 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;
|
|
|
|
-- Full sort, not just incremental sort can be pushed below a gather merge path
|
|
-- by generate_useful_gather_paths.
|
|
explain (costs off) select distinct a,b from t;
|
|
|
|
drop table t;
|
|
|
|
-- Sort pushdown can't go below where expressions are part of the rel target.
|
|
-- In particular this is interesting for volatile expressions which have to
|
|
-- go above joins since otherwise we'll incorrectly use expression evaluations
|
|
-- across multiple rows.
|
|
set enable_hashagg=off;
|
|
set enable_seqscan=off;
|
|
set enable_incremental_sort = off;
|
|
set parallel_tuple_cost=0;
|
|
set parallel_setup_cost=0;
|
|
set min_parallel_table_scan_size = 0;
|
|
set min_parallel_index_scan_size = 0;
|
|
|
|
-- Parallel sort below join.
|
|
explain (costs off) select distinct sub.unique1, stringu1
|
|
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
|
|
explain (costs off) select sub.unique1, stringu1
|
|
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
|
|
order by 1, 2;
|
|
-- Parallel sort but with expression that can be safely generated at the base rel.
|
|
explain (costs off) select distinct sub.unique1, md5(stringu1)
|
|
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
|
|
explain (costs off) select sub.unique1, md5(stringu1)
|
|
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
|
|
order by 1, 2;
|
|
-- Parallel sort but with expression (correlated subquery) that
|
|
-- is prohibited in parallel plans.
|
|
explain (costs off) select distinct
|
|
unique1,
|
|
(select t.unique1 from tenk1 where tenk1.unique1 = t.unique1)
|
|
from tenk1 t, generate_series(1, 1000);
|
|
explain (costs off) select
|
|
unique1,
|
|
(select t.unique1 from tenk1 where tenk1.unique1 = t.unique1)
|
|
from tenk1 t, generate_series(1, 1000)
|
|
order by 1, 2;
|
|
-- Parallel sort but with expression not available until the upper rel.
|
|
explain (costs off) select distinct sub.unique1, stringu1 || random()::text
|
|
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
|
|
explain (costs off) select sub.unique1, stringu1 || random()::text
|
|
from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
|
|
order by 1, 2;
|
|
-- Disallow pushing down sort when pathkey is an SRF.
|
|
explain (costs off) select unique1 from tenk1 order by unnest('{1,2}'::int[]);
|