Thread: "union all" query consumes all memory
Hello,
one my customer reported a "out of memory" issue. After investigation he found a main problem in large query that uses a lot of union all queries. He wrote a self test:do $$
declare i integer; str text='';
begin
for i in 1..1000 loop
str := str || 'union all select i,i,i from generate_series(1,50000) g(i) ';
end loop;
execute 'select 1,2,3 ' || str;
end; $$
Pavel Stehule <pavel.stehule@gmail.com> writes:
> one my customer reported a "out of memory" issue. After investigation he
> found a main problem in large query that uses a lot of union all queries.
> He wrote a self test:
> do $$
> declare i integer; str text='';
> begin
> for i in 1..1000 loop
> str := str || 'union all select i,i,i from generate_series(1,50000) g(i) ';
> end loop;
> execute 'select 1,2,3 ' || str;
> end;
> $$
> is it expected behave?
Well, that query is entitled to use 1000 * work_mem for the
generate_series output tuplestores. What's your work_mem setting?
Perhaps more to the point, what was your customer doing?
regards, tom lane