Greetings,
I've been toying aroudn with postgres 7.1beta5's ability to control the
planner via explicitely JOINing tables. I then (just for giggles) compare the
difference in the EXPLAIN results.
I'm no super-mondo-DBA or anything, but in my two attempts so far, the numbers
I get out of EXPLAIN have been about 1/2 as small.
Below are two EXPLAIN results, am I correct in reading that one is indeed
"twice as fast" as the other? I say twice as fast because the top-most cost in
the first query is 58.62, but in the second one it's only 32.09. Am I reading
this correctly?
-- First EXPLAIN --
Sort (cost=58.62..58.62 rows=14 width=60)
-> Nested Loop (cost=0.00..58.35 rows=14)
-> Nested Loop (cost=0.00..29.99 rows=14)
-> Seq Scan on playlist p (cost=0.00..1.61 rows=14)
-> Index Scan using songs_pkey on songs s (cost=0.00..2.01 rows=1)
-> Index Scan using artists_pkey on artists a (cost=0.00..2.01 rows=1)
-- Second EXPLAIN --
Sort (cost=32.09..32.09 rows=1)
-> Nested Loop (cost=0.00..32.08 rows=1)
-> Nested Loop (cost=0.00..30.06 rows=1)
-> Seq Scan on playlist p (cost=0.00..1.61 rows=14)
-> Index Scan using songs_pkey on songs s (cost=0.00..2.02 rows=1)
-> Index Scan using artists_pkey on artists a (cost=0.00..2.01 rows=1)
-- Dave
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