Re: triple self-join crawling

Andrew Sullivan wrote:
> Define "crawling". Also, please post EXPLAIN and, if feasible,

Total runtime: 191430.537 ms

> EXPLAIN ANALYSE output for your case.
>
> On Sun, Mar 18, 2007 at 07:51:28PM +0000, T E Schmitz wrote:
>
>>The following self join of a table containing 5800 records is crawling:
>>
>>
>>SELECT
>> history.stock, history.day, history.high, history.low,
>> MAX(past_week.high) AS week_high,
>> MAX(past_month.high) AS month_high
>>FROM history
>>INNER JOIN history AS past_month ON (past_month.stock = history.stock
>>AND past_month.day < history.day AND past_month.day >= (history.day - 30))
>>INNER JOIN history AS past_week ON (past_week.stock =
>>past_month.stock AND past_week.day < history.day AND past_week.day >=
>>(history.day - 7))
>>GROUP BY history.stock, history.day, history.high, history.low
>>ORDER BY history.stock, history.day DESC

QUERY PLAN
GroupAggregate (cost=1372725715.71..1414901439.85 rows=5801 width=56)
(actual time=185248.481..191393.056 rows=5800 loops=1)
-> Sort (cost=1372725715.71..1378750806.73 rows=2410036407
width=56) (actual time=185247.212..187763.008 rows=584203 loops=1)
Sort Key: history.stock, history."day", history.high, history.low
-> Nested Loop (cost=0.00..132245248.41 rows=2410036407
width=56) (actual time=0.124..148136.464 rows=584203 loops=1)
Join Filter: (("inner".stock)::text = ("outer".stock)::text)
-> Nested Loop (cost=0.00..555931.84 rows=3739067
width=53) (actual time=0.087..137531.941 rows=28147 loops=1)
Join Filter: (("outer"."day" >= ("inner"."day" -
7)) AND (("outer".stock)::text = ("inner".stock)::text))
-> Index Scan using history_pkey on history
past_week (cost=0.00..266.62 rows=5801 width=23) (actual
time=0.034..43.147 rows=5801 loops=1)
-> Index Scan using idx_history_day on history
(cost=0.00..57.11 rows=1934 width=34) (actual time=0.021..12.709
rows=2900 loops=5801)
Index Cond: ("outer"."day" < history."day")
-> Index Scan using idx_history_day on history
past_month (cost=0.00..22.32 rows=645 width=23) (actual
time=0.019..0.170 rows=21 loops=28147)
Index Cond: ((past_month."day" < "outer"."day") AND
(past_month."day" >= ("outer"."day" - 30)))
Total runtime: 191430.537 ms

--

Regards,

Tarlika Elisabeth Schmitz