In my application we are using postgresql,now it has one million records in summary table.
When I run the following query it takes 80,927 ms
SELECT COUNT(*) AS count
FROM summary_views
GROUP BY question_id,category_type_id
Is there any efficient way to do this?
COUNT(*) in PostgreSQL tends to be slow. It's a feature of MVCC. One of the workarounds of the problem is a row counting trigger with a helper table:
create table table_count(
table_count_id text primary key,
rows int default 0
);
CREATE OR REPLACE FUNCTION table_count_update()
RETURNS trigger AS
$BODY$
begin
if tg_op = 'INSERT' then
update table_count set rows = rows + 1
where table_count_id = TG_TABLE_NAME;
elsif tg_op = 'DELETE' then
update table_count set rows = rows - 1
where table_count_id = TG_TABLE_NAME;
end if;
return null;
end;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
Next step is to add proper trigger declaration for each table you'd like to use it with. For example for table tab_name:
begin;
insert into table_count values
('tab_name',(select count(*) from tab_name));
create trigger tab_name_table_count after insert or delete
on tab_name for each row execute procedure table_count_update();
commit;
It is important to run in a transaction block to keep actual count and helper table in sync in case of delete or insert between initial count and trigger creation. Transaction guarantees this. From now on to get current count instantly, just invoke:
select rows from table_count where table_count_id = 'tab_name';
Edit: In case of your group by clause, you'll need more sophisticated trigger function and count table.
EXPLAIN (ANALYZE, BUFFERS)for the query, there is not one can say. See wiki.postgresql.org/wiki/Slow_Query_Questions