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From: Scott Ribe <[email protected]>
To: Rui DeSousa <[email protected]>
Cc: Pgsql-admin <[email protected]>
Cc: Tom Lane <[email protected]>
Subject: Re: update behavior
Date: Thu, 19 Jun 2025 11:58:36 -0600
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

> On Jun 19, 2025, at 11:54 AM, Rui DeSousa <[email protected]> wrote:
> 
> 
> 
>> On Jun 19, 2025, at 1:23 PM, Scott Ribe <[email protected]> wrote:
>> 
>> I believe that if I UPDATE a row with the same values that it already has, this still dirties pages, writes the row, generates a WAL entry. There is no shortcut in the processing that's "hey, there's not really a change here, we'll just leave storage alone".
>> 
>> Is this correct?
>> 
> 
> Correct, but it can be avoided. 
> 
> No update occurs in this case:. 
> 
> update foo
>   set data = ‘hello world’
> where id = 33
>    and data is distinct from ‘hello world’
> ;

That was my thought when I posted the original question, when I didn't know about suppress_redundant_updates_trigger. Now I'm thinking the trigger is an option.

- The trigger has the advantage that one doesn't have to maintain the WHERE clause--especially if the list of columns is long.
- It has the disadvantage of always running, even in contexts where it might not be needed.

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