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
usingidx_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