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In-Reply-To: <9ee6324a-44fc-42fb-bf8e-7c3b53395588@iki.fi>
From: Maxim Orlov <orlovmg@gmail.com>
Date: Wed, 26 Nov 2025 18:23:18 +0300
Message-ID: 
 <CACG=ezY0=ri8A0duXbpd1XNUc1jnngaPnmB0-+UZpxAv7-fNtw@mail.gmail.com>
Subject: Re: POC: make mxidoff 64 bits
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>,
 Alexander Korotkov <aekorotkov@gmail.com>,
	wenhui qiu <qiuwenhuifx@gmail.com>,
	Postgres hackers <pgsql-hackers@lists.postgresql.org>,
	Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
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On Tue, 25 Nov 2025 at 13:07, Heikki Linnakangas <hlinnaka@iki.fi> wrote:

>
> GetOldMultiXactIdSingleMember() currently asserts that the offset is
> never zero, but it should try to do something sensible in that case
> instead of just failing.
>
> Correct me if I'm wrong, but we added the assertion that offsets are
never 0, based on the idea that case #2 will never take place during an
update. If this isn't the case, this assertion could be removed.
The rest of the function appears to work correctly.

I even think that, as an experiment, we could randomly reset some of the
offsets to zero and nothing would happen, except that some data would
be lost.

The most sensible thing we can do is give the user a warning, right?
Something like, "During the update, we encountered some weird offset
that shouldn't have been there, but there's nothing we can do about it,
just take note."

-- 
Best regards,
Maxim Orlov.

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><div class=3D"gmail_quote gmail=
_quote_container"><div dir=3D"ltr" class=3D"gmail_attr">On Tue, 25 Nov 2025=
 at 13:07, Heikki Linnakangas &lt;<a href=3D"mailto:hlinnaka@iki.fi">hlinna=
ka@iki.fi</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex">=C2=A0<br>
GetOldMultiXactIdSingleMember() currently asserts that the offset is <br>
never zero, but it should try to do something sensible in that case <br>
instead of just failing.<br><br>
</blockquote></div><div>Correct me if I&#39;m wrong, but we added the asser=
tion that offsets are<br>never 0, based on the idea that case #2 will never=
 take place during an<br>update. If this isn&#39;t the case, this assertion=
 could be removed.<br>The rest of the function appears to work correctly.<b=
r><br>I even think that, as an experiment, we could randomly reset some of =
the<br>offsets to zero and nothing would happen, except that some data woul=
d</div><div>be lost.<br><br>The most sensible thing we can do is give the u=
ser a warning, right?<br>Something like, &quot;During the update, we encoun=
tered some weird offset<br>that shouldn&#39;t have been there, but there=
9;s nothing we can do about it,<br>just take note.&quot;</div><br><span cla=
ss=3D"gmail_signature_prefix">-- </span><br><div dir=3D"ltr" class=3D"gmail=
_signature"><div dir=3D"ltr"><div>Best regards,<br></div><div>Maxim Orlov.<=
/div></div></div></div>

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