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From: William Alves Da Silva <[email protected]>
To: Tim Schwenke <[email protected]>
Cc: pgsql-novice <[email protected]>
Subject: Re: Does PostgreSQL cache all columns of a table after SELECT?
Date: Mon, 5 Jun 2023 09:19:53 -0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Hello Tim,

Can you send the EXPLAIN (BUFFERS, ANALYZE, VERBOSE) of your query? This will show you whether the plan is using caching or not.


> On 5 Jun 2023, at 09:15, Tim Schwenke <[email protected]> wrote:
> 
> Hello,
> 
> I have the following table with the following columns:
> 
> large_a: text (few dozen characters up to a few hundred)
> large_b: text (few dozen characters up to a few hundred)
> 
> The table has several million rows. The DB is running on a large machine.
> 
> I perform the following query:
> 
> select large_a from table;
> 
> The first query takes a few minutes. Afterwards I see that the cache in memory has grown. Next query only takes a few seconds.
> 
> What I want to know:
> 
> Does the cache also contain large_b? Or is only large_a cached? Assumption is that memory is large enough to fit everything.
> 
> 
> 

Regards,
William Alves

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