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From: "David G. Johnston" <david.g.johnston@gmail.com>
Date: Wed, 11 May 2022 10:00:15 -0700
Message-ID: 
 <CAKFQuwaxozDM-+P-nKPY1aBZ0feckRQbAQJ=d8HJtv8-E8TzQg@mail.gmail.com>
Subject: Re: SET TRANSACTION SNAPSHOT sounds like replicated environment but
 isn't
To: maweki@gmail.com, Pg Docs <pgsql-docs@lists.postgresql.org>
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On Wed, May 11, 2022 at 7:33 AM PG Doc comments form <noreply@postgresql.org>
wrote:

> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/14/sql-set-transaction.html
> Description:
>
> Hello,
>
> the wording on the SET TRANSACTION SNAPSHOT left me a bit confused. It says
> "To begin a new transaction with the same snapshot as an already existing
> transaction" and it feels like basically taking over an existing
> session/transaction or being able to replicate a transaction from that
> snapshot on.
>

I'm not sure what a final documentation patch might look like but this
section can rightfully assume some prior knowledge about how the system
works with regards to snapshots.  In particular, a snapshot is effectively
a single value that a session maintains that lets it compute whether a
given transaction id is visible or not.  So, "whenever you give me data
only do so up to this point-in-time".  Understanding that dynamic should
lead one to conclude that just having a shared since of "point-in-time"
doesn't have anything to do with permissions to interact with specific
objects in the first place.  And, for temporary tables, to break the
session isolation that it is assumed the reader is aware of.

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 Wed, May 11, 2022 at 7:33 AM PG Doc comments form &lt;<=
a href=3D"mailto:noreply@postgresql.org">noreply@postgresql.org</a>&gt; wro=
te:</span><br></div></div><div class=3D"gmail_quote"><blockquote class=3D"g=
mail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204=
,204,204);padding-left:1ex">The following documentation comment has been lo=
gged on the website:<br>
<br>
Page: <a href=3D"https://www.postgresql.org/docs/14/sql-set-transaction.htm=
l" rel=3D"noreferrer" target=3D"_blank">https://www.postgresql.org/docs/14/=
sql-set-transaction.html</a><br>
Description:<br>
<br>
Hello,<br>
<br>
the wording on the SET TRANSACTION SNAPSHOT left me a bit confused. It says=
<br>
&quot;To begin a new transaction with the same snapshot as an already exist=
ing<br>
transaction&quot; and it feels like basically taking over an existing<br>
session/transaction or being able to replicate a transaction from that<br>
snapshot on.<br></blockquote><div><br></div><div class=3D"gmail_default" st=
yle=3D"font-family:arial,helvetica,sans-serif">I&#39;m not sure what a fina=
l documentation patch might look like but this section can rightfully assum=
e some prior knowledge about how the system works with regards to snapshots=
.=C2=A0 In particular, a snapshot is effectively a single value that a sess=
ion maintains that lets it compute whether a given transaction id is visibl=
e or not.=C2=A0 So, &quot;whenever you give me data only do so up to this p=
oint-in-time&quot;.=C2=A0 Understanding that dynamic should lead one to con=
clude that just having a shared since of &quot;point-in-time&quot; doesn=
9;t have anything to do with permissions to interact with specific objects =
in the first place.=C2=A0 And, for temporary tables, to break the session i=
solation that it is assumed the reader is aware of.</div><div class=3D"gmai=
l_default" style=3D"font-family:arial,helvetica,sans-serif"><br></div><div =
class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif">Da=
vid J.</div><div class=3D"gmail_default" style=3D"font-family:arial,helveti=
ca,sans-serif"><br></div></div></div>

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