Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Slow query on a one-tuple table
To: Michael Lewis <mlewis@entrata.com>
References: 
 <CA+t6e1kacbVHq69aihEVeBzH_nMY5eK7bZ-UXL_FuUquEgF_gg@mail.gmail.com>
 <24571.1568910502@sss.pgh.pa.us>
 <774d6080-d6d7-e9e7-7351-9a412c7d5956@siscobra.com.br>
 <CAHOFxGqMpUxn54jMLoU4-HcUata2yfLgjEbRHdJG3k0BBDPbog@mail.gmail.com>
 <ab6ea98e-6266-7665-40b7-151c5736c08d@siscobra.com.br>
 <BN6PR1701MB1890E31E15D486A85FEC8510DA890@BN6PR1701MB1890.namprd17.prod.outlook.com>
From: =?UTF-8?Q?Lu=c3=ads_Roberto_Weck?= <luisroberto@siscobra.com.br>
Message-ID: <bf03aedc-9201-f7c9-ef25-e795d4e1626a@siscobra.com.br>
Date: Thu, 19 Sep 2019 16:59:01 -0300
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.9.0
MIME-Version: 1.0
In-Reply-To: 
 <BN6PR1701MB1890E31E15D486A85FEC8510DA890@BN6PR1701MB1890.namprd17.prod.outlook.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: pt-BR
Precedence: bulk

Em 19/09/2019 15:34, Igor Neyman escreveu:
> -----Original Message-----
> From: Luís Roberto Weck [mailto:luisroberto@siscobra.com.br]
> Sent: Thursday, September 19, 2019 2:30 PM
> To: Michael Lewis <mlewis@entrata.com>
> Cc: pgsql-performance@lists.postgresql.org
> Subject: Re: Slow query on a one-tuple table
>
> WARNING: This email originated from outside of Perceptron! Please be mindful of PHISHING and MALWARE risks.
>
> 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
>
> ________________________________________________________________________________________________________________
>
> 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.