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10fcb83da6
switchToPresortedPrefixMode() did the wrong thing if it detected a batch boundary just at the last tuple of a fullsort group. The initially-reported symptom was a "retrieved too many tuples in a bounded sort" error, but the test case added here just silently gives the wrong answer without this patch. I (tgl) am not really happy about committing this patch without review from the incremental-sort authors, but they seem AWOL and we are hard against a release deadline. This does demonstrably make some cases better, anyway. Per bug #16846 from Yoran Heling. Back-patch to v13 where incremental sort was introduced. Neil Chen Discussion: https://postgr.es/m/16846-ae49f51ac379a4cb@postgresql.org
275 lines
12 KiB
PL/PgSQL
275 lines
12 KiB
PL/PgSQL
-- When we have to sort the entire table, incremental sort will
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-- be slower than plain sort, so it should not be used.
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explain (costs off)
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select * from (select * from tenk1 order by four) t order by four, ten;
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-- When there is a LIMIT clause, incremental sort is beneficial because
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-- it only has to sort some of the groups, and not the entire table.
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explain (costs off)
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select * from (select * from tenk1 order by four) t order by four, ten
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limit 1;
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-- When work_mem is not enough to sort the entire table, incremental sort
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-- may be faster if individual groups still fit into work_mem.
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set work_mem to '2MB';
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explain (costs off)
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select * from (select * from tenk1 order by four) t order by four, ten;
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reset work_mem;
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create table t(a integer, b integer);
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create or replace function explain_analyze_without_memory(query text)
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returns table (out_line text) language plpgsql
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as
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$$
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declare
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line text;
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begin
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for line in
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execute 'explain (analyze, costs off, summary off, timing off) ' || query
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loop
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out_line := regexp_replace(line, '\d+kB', 'NNkB', 'g');
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return next;
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end loop;
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end;
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$$;
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create or replace function explain_analyze_inc_sort_nodes(query text)
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returns jsonb language plpgsql
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as
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$$
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declare
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elements jsonb;
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element jsonb;
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matching_nodes jsonb := '[]'::jsonb;
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begin
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execute 'explain (analyze, costs off, summary off, timing off, format ''json'') ' || query into strict elements;
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while jsonb_array_length(elements) > 0 loop
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element := elements->0;
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elements := elements - 0;
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case jsonb_typeof(element)
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when 'array' then
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if jsonb_array_length(element) > 0 then
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elements := elements || element;
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end if;
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when 'object' then
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if element ? 'Plan' then
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elements := elements || jsonb_build_array(element->'Plan');
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element := element - 'Plan';
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else
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if element ? 'Plans' then
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elements := elements || jsonb_build_array(element->'Plans');
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element := element - 'Plans';
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end if;
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if (element->>'Node Type')::text = 'Incremental Sort' then
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matching_nodes := matching_nodes || element;
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end if;
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end if;
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end case;
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end loop;
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return matching_nodes;
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end;
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$$;
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create or replace function explain_analyze_inc_sort_nodes_without_memory(query text)
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returns jsonb language plpgsql
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as
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$$
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declare
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nodes jsonb := '[]'::jsonb;
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node jsonb;
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group_key text;
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space_key text;
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begin
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for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
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for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
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for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
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node := jsonb_set(node, array[group_key, space_key, 'Average Sort Space Used'], '"NN"', false);
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node := jsonb_set(node, array[group_key, space_key, 'Peak Sort Space Used'], '"NN"', false);
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end loop;
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end loop;
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nodes := nodes || node;
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end loop;
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return nodes;
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end;
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$$;
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create or replace function explain_analyze_inc_sort_nodes_verify_invariants(query text)
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returns bool language plpgsql
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as
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$$
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declare
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node jsonb;
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group_stats jsonb;
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group_key text;
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space_key text;
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begin
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for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
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for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
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group_stats := node->group_key;
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for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
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if (group_stats->space_key->'Peak Sort Space Used')::bigint < (group_stats->space_key->'Peak Sort Space Used')::bigint then
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raise exception '% has invalid max space < average space', group_key;
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end if;
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end loop;
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end loop;
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end loop;
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return true;
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end;
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$$;
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-- A single large group tested around each mode transition point.
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insert into t(a, b) select i/100 + 1, i + 1 from generate_series(0, 999) n(i);
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analyze t;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 31;
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select * from (select * from t order by a) s order by a, b limit 31;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
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select * from (select * from t order by a) s order by a, b limit 32;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
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select * from (select * from t order by a) s order by a, b limit 33;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
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select * from (select * from t order by a) s order by a, b limit 65;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
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select * from (select * from t order by a) s order by a, b limit 66;
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delete from t;
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-- An initial large group followed by a small group.
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insert into t(a, b) select i/50 + 1, i + 1 from generate_series(0, 999) n(i);
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analyze t;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 55;
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select * from (select * from t order by a) s order by a, b limit 55;
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-- Test EXPLAIN ANALYZE with only a fullsort group.
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select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 55');
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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'));
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select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 55');
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delete from t;
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-- An initial small group followed by a large group.
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insert into t(a, b) select (case when i < 5 then i else 9 end), i from generate_series(1, 1000) n(i);
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analyze t;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 70;
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select * from (select * from t order by a) s order by a, b limit 70;
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-- Checks case where we hit a group boundary at the last tuple of a batch.
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select * from (select * from t order by a) s order by a, b limit 5;
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-- Test rescan.
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begin;
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-- We force the planner to choose a plan with incremental sort on the right side
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-- of a nested loop join node. That way we trigger the rescan code path.
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set local enable_hashjoin = off;
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set local enable_mergejoin = off;
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set local enable_material = off;
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set local enable_sort = off;
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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);
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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);
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rollback;
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-- Test EXPLAIN ANALYZE with both fullsort and presorted groups.
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select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 70');
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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'));
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select explain_analyze_inc_sort_nodes_verify_invariants('select * from (select * from t order by a) s order by a, b limit 70');
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delete from t;
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-- Small groups of 10 tuples each tested around each mode transition point.
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insert into t(a, b) select i / 10, i from generate_series(1, 1000) n(i);
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analyze t;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 31;
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select * from (select * from t order by a) s order by a, b limit 31;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
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select * from (select * from t order by a) s order by a, b limit 32;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
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select * from (select * from t order by a) s order by a, b limit 33;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
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select * from (select * from t order by a) s order by a, b limit 65;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
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select * from (select * from t order by a) s order by a, b limit 66;
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delete from t;
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-- Small groups of only 1 tuple each tested around each mode transition point.
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insert into t(a, b) select i, i from generate_series(1, 1000) n(i);
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analyze t;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 31;
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select * from (select * from t order by a) s order by a, b limit 31;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 32;
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select * from (select * from t order by a) s order by a, b limit 32;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 33;
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select * from (select * from t order by a) s order by a, b limit 33;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 65;
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select * from (select * from t order by a) s order by a, b limit 65;
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explain (costs off) select * from (select * from t order by a) s order by a, b limit 66;
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select * from (select * from t order by a) s order by a, b limit 66;
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delete from t;
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drop table t;
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-- Incremental sort vs. parallel queries
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set min_parallel_table_scan_size = '1kB';
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set min_parallel_index_scan_size = '1kB';
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set parallel_setup_cost = 0;
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set parallel_tuple_cost = 0;
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set max_parallel_workers_per_gather = 2;
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create table t (a int, b int, c int);
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insert into t select mod(i,10),mod(i,10),i from generate_series(1,10000) s(i);
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create index on t (a);
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analyze t;
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set enable_incremental_sort = off;
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explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1;
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set enable_incremental_sort = on;
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explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1;
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-- Incremental sort vs. set operations with varno 0
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set enable_hashagg to off;
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explain (costs off) select * from t union select * from t order by 1,3;
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-- Full sort, not just incremental sort can be pushed below a gather merge path
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-- by generate_useful_gather_paths.
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explain (costs off) select distinct a,b from t;
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drop table t;
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-- Sort pushdown can't go below where expressions are part of the rel target.
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-- In particular this is interesting for volatile expressions which have to
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-- go above joins since otherwise we'll incorrectly use expression evaluations
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-- across multiple rows.
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set enable_hashagg=off;
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set enable_seqscan=off;
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set enable_incremental_sort = off;
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set parallel_tuple_cost=0;
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set parallel_setup_cost=0;
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set min_parallel_table_scan_size = 0;
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set min_parallel_index_scan_size = 0;
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-- Parallel sort below join.
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explain (costs off) select distinct sub.unique1, stringu1
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from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
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explain (costs off) select sub.unique1, stringu1
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from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
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order by 1, 2;
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-- Parallel sort but with expression that can be safely generated at the base rel.
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explain (costs off) select distinct sub.unique1, md5(stringu1)
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from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
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explain (costs off) select sub.unique1, md5(stringu1)
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from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
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order by 1, 2;
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-- Parallel sort but with expression (correlated subquery) that
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-- is prohibited in parallel plans.
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explain (costs off) select distinct
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unique1,
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(select t.unique1 from tenk1 where tenk1.unique1 = t.unique1)
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from tenk1 t, generate_series(1, 1000);
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explain (costs off) select
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unique1,
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(select t.unique1 from tenk1 where tenk1.unique1 = t.unique1)
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from tenk1 t, generate_series(1, 1000)
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order by 1, 2;
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-- Parallel sort but with expression not available until the upper rel.
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explain (costs off) select distinct sub.unique1, stringu1 || random()::text
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from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
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explain (costs off) select sub.unique1, stringu1 || random()::text
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from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
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order by 1, 2;
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-- Disallow pushing down sort when pathkey is an SRF.
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explain (costs off) select unique1 from tenk1 order by unnest('{1,2}'::int[]);
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