Re: Dataset is fetched from cache but still takes same time to fetch records as first run

From: Dave Stibrany <dstibrany(at)gmail(dot)com>
To: Sumeet Shukla <sumeet(dot)k(dot)shukla(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Dataset is fetched from cache but still takes same time to fetch records as first run
Date: 2017-06-23 00:54:41
Message-ID: CAK17Jmm6WBXy-4-_H21PAopoU5o=FyoLwjBkPeJCNHCU59z-Qw@mail.gmail.com
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The numbers you posted look exactly as I would expect. The first read hits
disk and takes 108ms, the second read hits the cache and takes 27ms.

On Thu, Jun 22, 2017 at 8:40 PM, Sumeet Shukla <sumeet(dot)k(dot)shukla(at)gmail(dot)com>
wrote:

> Both the first run and subsequent run takes same amount of time.
>
> *First Run:*
>
> "Seq Scan on d_payer (cost=0.00..8610.40 rows=121788 width=133) (actual
> time=8.760..98.582 rows=121788 loops=1)"
> " *Buffers: shared read=2521*"
> "Planning time: 16.820 ms"
> "Execution time: 108.626 ms"
>
>
> *Second Run:*
>
> "Seq Scan on d_payer (cost=0.00..8610.40 rows=121788 width=133) (actual
> time=0.010..18.456 rows=121788 loops=1)"
> " *Buffers: shared hit=2521*"
> "Planning time: 0.083 ms"
> "Execution time: 27.288 ms"
>
>
> Can anyone please help me understand and fix this.
>
>
> Thanks & Regards,
> Sumeet Shukla
>
>

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