Question

I’m trying to figure out a way to speed up a particularly cumbersome query which aggregates some data by date across a couple of tables. The full (ugly) query is below along with an EXPLAIN ANALYZE to show just how horrible it is.

If anyone could take a peek and see if they can spot any major issues (which is likely, I’m not a Postgres guy) that would be superb.

So here goes. The query is:

SELECT 
 to_char(p.period, 'DD/MM/YY') as period,
 coalesce(o.value, 0) AS outbound,
 coalesce(i.value, 0) AS inbound
FROM (
 SELECT
  date '2009-10-01' + s.day 
  AS period 
  FROM generate_series(0, date '2009-10-31' - date '2009-10-01') AS s(day)
) AS p 
LEFT OUTER JOIN(
 SELECT
  SUM(b.body_size) AS value, 
  b.body_time::date AS period 
 FROM body AS b 
 LEFT JOIN 
  envelope e ON e.message_id = b.message_id 
 WHERE 
  e.envelope_command = 1 
  AND b.body_time BETWEEN '2009-10-01' 
  AND (date '2009-10-31' + INTERVAL '1 DAY') 
 GROUP BY period 
 ORDER BY period
) AS o ON p.period = o.period
LEFT OUTER JOIN( 
 SELECT 
  SUM(b.body_size) AS value, 
  b.body_time::date AS period 
 FROM body AS b 
 LEFT JOIN 
  envelope e ON e.message_id = b.message_id 
 WHERE 
  e.envelope_command = 2 
  AND b.body_time BETWEEN '2009-10-01' 
  AND (date '2009-10-31' + INTERVAL '1 DAY') 
 GROUP BY period 
 ORDER BY period
) AS i ON p.period = i.period 

The EXPLAIN ANALYZE can be found here: on explain.depesz.com

Any comments or questions are appreciated.

Cheers

Answer 1

Building on Craig Young’s suggestions, here is the amended query which runs in ~1.8 seconds for the data set I’m working on. That is a slight improvement on the original ~2.0s and a huge improvement on Craig’s which took ~22s.

SELECT
    p.period,
    /* The pivot technique... */
    SUM(CASE envelope_command WHEN 1 THEN body_size ELSE 0 END) AS Outbound,
    SUM(CASE envelope_command WHEN 2 THEN body_size ELSE 0 END) AS Inbound
FROM
(
    /* Get days range */
    SELECT date '2009-10-01' + day AS period
    FROM generate_series(0, date '2009-10-31' - date '2009-10-01') AS day
) p
    /* Join message information */
    LEFT OUTER JOIN
    (
        SELECT b.body_size, b.body_time::date, e.envelope_command
        FROM body AS b 
            INNER JOIN envelope e ON e.message_id = b.message_id 
        WHERE
            e.envelope_command IN (2, 1)
            AND b.body_time::date BETWEEN (date '2009-10-01') AND (date '2009-10-31')
    ) d ON d.body_time = p.period
GROUP BY p.period
ORDER BY p.period