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From: "David G. Johnston" <david.g.johnston@gmail.com>
Date: Thu, 19 Jun 2025 10:31:59 -0700
Message-ID: 
 <CAKFQuwbwAbbk6KUKXyX2VxpX3aUDhS5Zd__2JKQXdhH5zHaB4g@mail.gmail.com>
Subject: Re: update behavior
To: Scott Ribe <scott_ribe@elevated-dev.com>
Cc: Pgsql-admin <pgsql-admin@lists.postgresql.org>
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On Thu, Jun 19, 2025 at 10:24=E2=80=AFAM Scott Ribe <scott_ribe@elevated-de=
v.com>
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.  You need a trigger to prevent the update.  There is one provided:
suppress_redundant_updates_trigger()

https://www.postgresql.org/docs/17/functions-trigger.html

David J.

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<div dir=3D"ltr"><div dir=3D"ltr"><div class=3D"gmail_default" style=3D"fon=
t-family:arial,helvetica,sans-serif"><span style=3D"font-family:Arial,Helve=
tica,sans-serif">On Thu, Jun 19, 2025 at 10:24=E2=80=AFAM Scott Ribe &lt;<a=
 href=3D"mailto:scott_ribe@elevated-dev.com">scott_ribe@elevated-dev.com</a=
>&gt; wrote:</span></div></div><div class=3D"gmail_quote gmail_quote_contai=
ner"><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bo=
rder-left:1px solid rgb(204,204,204);padding-left:1ex">I believe that if I =
UPDATE a row with the same values that it already has, this still dirties p=
ages, writes the row, generates a WAL entry. There is no shortcut in the pr=
ocessing that&#39;s &quot;hey, there&#39;s not really a change here, we&#39=
;ll just leave storage alone&quot;.<br>
<br>
Is this correct?<br><br></blockquote><div><br></div><div class=3D"gmail_def=
ault" style=3D"font-family:arial,helvetica,sans-serif">Correct.=C2=A0 You n=
eed a trigger to prevent the update.=C2=A0 There is one provided: suppress_=
redundant_updates_trigger()</div><div class=3D"gmail_default" style=3D"font=
-family:arial,helvetica,sans-serif"><br></div><div class=3D"gmail_default" =
style=3D"font-family:arial,helvetica,sans-serif"><a href=3D"https://www.pos=
tgresql.org/docs/17/functions-trigger.html">https://www.postgresql.org/docs=
/17/functions-trigger.html</a></div><div class=3D"gmail_default" style=3D"f=
ont-family:arial,helvetica,sans-serif"><br></div><div class=3D"gmail_defaul=
t" style=3D"font-family:arial,helvetica,sans-serif">David J.</div><div clas=
s=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif"><br></=
div></div></div>

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