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Share transition state between different aggregates when possible.
If there are two different aggregates in the query with same inputs, and the aggregates have the same initial condition and transition function, only calculate the state value once, and only call the final functions separately. For example, AVG(x) and SUM(x) aggregates have the same transition function, which accumulates the sum and number of input tuples. For a query like "SELECT AVG(x), SUM(x) FROM x", we can therefore accumulate the state function only once, which gives a nice speedup. David Rowley, reviewed and edited by me.
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Heikki Linnakangas
@ -1580,3 +1580,207 @@ select least_agg(variadic array[q1,q2]) from int8_tbl;
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-4567890123456789
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(1 row)
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-- test aggregates with common transition functions share the same states
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begin work;
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create type avg_state as (total bigint, count bigint);
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create or replace function avg_transfn(state avg_state, n int) returns avg_state as
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$$
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declare new_state avg_state;
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begin
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raise notice 'avg_transfn called with %', n;
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if state is null then
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if n is not null then
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new_state.total := n;
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new_state.count := 1;
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return new_state;
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end if;
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return null;
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elsif n is not null then
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state.total := state.total + n;
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state.count := state.count + 1;
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return state;
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end if;
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return null;
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end
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$$ language plpgsql;
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create function avg_finalfn(state avg_state) returns int4 as
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$$
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begin
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if state is null then
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return NULL;
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else
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return state.total / state.count;
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end if;
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end
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$$ language plpgsql;
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create function sum_finalfn(state avg_state) returns int4 as
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$$
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begin
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if state is null then
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return NULL;
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else
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return state.total;
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end if;
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end
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$$ language plpgsql;
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create aggregate my_avg(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = avg_finalfn
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);
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create aggregate my_sum(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = sum_finalfn
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);
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-- aggregate state should be shared as aggs are the same.
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select my_avg(one),my_avg(one) from (values(1),(3)) t(one);
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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my_avg | my_avg
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--------+--------
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2 | 2
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(1 row)
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-- aggregate state should be shared as transfn is the same for both aggs.
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select my_avg(one),my_sum(one) from (values(1),(3)) t(one);
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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my_avg | my_sum
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--------+--------
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2 | 4
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(1 row)
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-- shouldn't share states due to the distinctness not matching.
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select my_avg(distinct one),my_sum(one) from (values(1),(3)) t(one);
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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my_avg | my_sum
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--------+--------
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2 | 4
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(1 row)
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-- shouldn't share states due to the filter clause not matching.
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select my_avg(one) filter (where one > 1),my_sum(one) from (values(1),(3)) t(one);
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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NOTICE: avg_transfn called with 3
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my_avg | my_sum
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--------+--------
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3 | 4
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(1 row)
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-- this should not share the state due to different input columns.
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select my_avg(one),my_sum(two) from (values(1,2),(3,4)) t(one,two);
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NOTICE: avg_transfn called with 2
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 4
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NOTICE: avg_transfn called with 3
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my_avg | my_sum
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--------+--------
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2 | 6
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(1 row)
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-- test that aggs with the same sfunc and initcond share the same agg state
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create aggregate my_sum_init(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = sum_finalfn,
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initcond = '(10,0)'
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);
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create aggregate my_avg_init(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = avg_finalfn,
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initcond = '(10,0)'
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);
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create aggregate my_avg_init2(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = avg_finalfn,
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initcond = '(4,0)'
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);
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-- state should be shared if INITCONDs are matching
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select my_sum_init(one),my_avg_init(one) from (values(1),(3)) t(one);
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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my_sum_init | my_avg_init
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-------------+-------------
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14 | 7
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(1 row)
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-- Varying INITCONDs should cause the states not to be shared.
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select my_sum_init(one),my_avg_init2(one) from (values(1),(3)) t(one);
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 1
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NOTICE: avg_transfn called with 3
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NOTICE: avg_transfn called with 3
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my_sum_init | my_avg_init2
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-------------+--------------
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14 | 4
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(1 row)
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rollback;
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-- test aggregate state sharing to ensure it works if one aggregate has a
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-- finalfn and the other one has none.
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begin work;
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create or replace function sum_transfn(state int4, n int4) returns int4 as
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$$
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declare new_state int4;
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begin
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raise notice 'sum_transfn called with %', n;
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if state is null then
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if n is not null then
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new_state := n;
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return new_state;
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end if;
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return null;
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elsif n is not null then
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state := state + n;
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return state;
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end if;
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return null;
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end
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$$ language plpgsql;
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create function halfsum_finalfn(state int4) returns int4 as
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$$
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begin
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if state is null then
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return NULL;
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else
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return state / 2;
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end if;
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end
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$$ language plpgsql;
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create aggregate my_sum(int4)
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(
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stype = int4,
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sfunc = sum_transfn
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);
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create aggregate my_half_sum(int4)
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(
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stype = int4,
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sfunc = sum_transfn,
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finalfunc = halfsum_finalfn
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);
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-- Agg state should be shared even though my_sum has no finalfn
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select my_sum(one),my_half_sum(one) from (values(1),(2),(3),(4)) t(one);
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NOTICE: sum_transfn called with 1
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NOTICE: sum_transfn called with 2
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NOTICE: sum_transfn called with 3
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NOTICE: sum_transfn called with 4
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my_sum | my_half_sum
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--------+-------------
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10 | 5
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(1 row)
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rollback;
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@ -590,3 +590,168 @@ drop view aggordview1;
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-- variadic aggregates
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select least_agg(q1,q2) from int8_tbl;
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select least_agg(variadic array[q1,q2]) from int8_tbl;
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-- test aggregates with common transition functions share the same states
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begin work;
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create type avg_state as (total bigint, count bigint);
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create or replace function avg_transfn(state avg_state, n int) returns avg_state as
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$$
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declare new_state avg_state;
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begin
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raise notice 'avg_transfn called with %', n;
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if state is null then
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if n is not null then
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new_state.total := n;
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new_state.count := 1;
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return new_state;
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end if;
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return null;
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elsif n is not null then
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state.total := state.total + n;
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state.count := state.count + 1;
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return state;
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end if;
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return null;
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end
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$$ language plpgsql;
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create function avg_finalfn(state avg_state) returns int4 as
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$$
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begin
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if state is null then
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return NULL;
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else
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return state.total / state.count;
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end if;
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end
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$$ language plpgsql;
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create function sum_finalfn(state avg_state) returns int4 as
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$$
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begin
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if state is null then
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return NULL;
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else
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return state.total;
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end if;
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end
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$$ language plpgsql;
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create aggregate my_avg(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = avg_finalfn
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);
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create aggregate my_sum(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = sum_finalfn
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);
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-- aggregate state should be shared as aggs are the same.
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select my_avg(one),my_avg(one) from (values(1),(3)) t(one);
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-- aggregate state should be shared as transfn is the same for both aggs.
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select my_avg(one),my_sum(one) from (values(1),(3)) t(one);
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-- shouldn't share states due to the distinctness not matching.
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select my_avg(distinct one),my_sum(one) from (values(1),(3)) t(one);
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-- shouldn't share states due to the filter clause not matching.
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select my_avg(one) filter (where one > 1),my_sum(one) from (values(1),(3)) t(one);
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-- this should not share the state due to different input columns.
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select my_avg(one),my_sum(two) from (values(1,2),(3,4)) t(one,two);
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-- test that aggs with the same sfunc and initcond share the same agg state
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create aggregate my_sum_init(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = sum_finalfn,
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initcond = '(10,0)'
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);
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create aggregate my_avg_init(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = avg_finalfn,
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initcond = '(10,0)'
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);
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create aggregate my_avg_init2(int4)
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(
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stype = avg_state,
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sfunc = avg_transfn,
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finalfunc = avg_finalfn,
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initcond = '(4,0)'
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);
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-- state should be shared if INITCONDs are matching
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select my_sum_init(one),my_avg_init(one) from (values(1),(3)) t(one);
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-- Varying INITCONDs should cause the states not to be shared.
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select my_sum_init(one),my_avg_init2(one) from (values(1),(3)) t(one);
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rollback;
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-- test aggregate state sharing to ensure it works if one aggregate has a
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-- finalfn and the other one has none.
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begin work;
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create or replace function sum_transfn(state int4, n int4) returns int4 as
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$$
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declare new_state int4;
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begin
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raise notice 'sum_transfn called with %', n;
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if state is null then
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if n is not null then
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new_state := n;
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return new_state;
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end if;
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return null;
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elsif n is not null then
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state := state + n;
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return state;
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end if;
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return null;
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end
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$$ language plpgsql;
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create function halfsum_finalfn(state int4) returns int4 as
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$$
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begin
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if state is null then
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return NULL;
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else
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return state / 2;
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end if;
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end
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$$ language plpgsql;
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create aggregate my_sum(int4)
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(
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stype = int4,
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sfunc = sum_transfn
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);
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create aggregate my_half_sum(int4)
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(
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stype = int4,
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sfunc = sum_transfn,
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finalfunc = halfsum_finalfn
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);
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-- Agg state should be shared even though my_sum has no finalfn
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select my_sum(one),my_half_sum(one) from (values(1),(2),(3),(4)) t(one);
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rollback;
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