Em 19/09/2019 15:34, Igor Neyman escreveu:
-----Original Message-----
From: Luís Roberto Weck [mailto:luisroberto@xxxxxxxxxxxxxxx]
Sent: Thursday, September 19, 2019 2:30 PM
To: Michael Lewis <mlewis@xxxxxxxxxxx>
Cc: pgsql-performance@xxxxxxxxxxxxxxxxxxxx
Subject: Re: Slow query on a one-tuple table
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Em 19/09/2019 14:21, Michael Lewis escreveu:
Is this result able to be repeated?
Yes, I can consistently repeat it.
Postgres version is 11.1.
Other executions:
Index Scan using assessoria_pkey on public.assessoria (cost=0.25..2.47
rows=1 width=62) (actual time=1.591..4.035 rows=1 loops=1)
Output: asscod, asscambol
Index Cond: (assessoria.asscod = 1)
Buffers: shared hit=1187
Planning Time: 0.053 ms
Execution Time: 4.055 ms
Index Scan using assessoria_pkey on public.assessoria (cost=0.25..2.47
rows=1 width=62) (actual time=1.369..3.838 rows=1 loops=1)
Output: asscod, asscambol
Index Cond: (assessoria.asscod = 1)
Buffers: shared hit=1187
Planning Time: 0.033 ms
Execution Time: 3.851 ms
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But can you repeat it with "LIMIT 1"?
Notice huge difference in "buffers hit" while doing (the same) Index Scan in two plans.
Regards,
Igor Neyman
With LIMIT 1, I get 3 shared buffers hit, pretty much always.
