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From: Ron Johnson <ronljohnsonjr@gmail.com>
Date: Wed, 10 Sep 2025 11:55:28 -0400
Message-ID: <CANzqJaAJ3NN5yv2FY+UBUm4vvz5y46yz=wK6LZaBtOsJ76KusA@mail.gmail.com>
Subject: Re: MVCC and all that...
To: pgsql-general <pgsql-general@postgresql.org>
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On Tue, Sep 9, 2025 at 8:41=E2=80=AFPM Justin <zzzzz.graf@gmail.com> wrote:
[snip]

> Multiple transactions per connection.  I am asking WHY is that a feature.
> when one can have multiple sessions, what is the difference?  running
> multiple transactions in single or multiple sessions means moving  part o=
f
> transaction logic into the application space. What do we gain here.....
>

If I interpret "Multiple transactions per connection" correctly, they're a
great way to emulate WITH HOLD cursors.

For example:
1. In channel #1, open a Read Only cursor.  (Yes, this was long ago.)
2. Fetch a row.
3. Switch to channel #2, begin R/W txn, modify the table, commit.
4. Switch back to channel #1
5. Go to step 2.

Not being an application developer anymore, I've never needed to use WITH
HOLD cursors or wish for multiple channels in PG.

--=20
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

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<div dir=3D"ltr"><div dir=3D"ltr">On Tue, Sep 9, 2025 at 8:41=E2=80=AFPM Ju=
stin &lt;<a href=3D"mailto:zzzzz.graf@gmail.com">zzzzz.graf@gmail.com</a>&g=
t; wrote:</div><div class=3D"gmail_quote gmail_quote_container"><div>[snip]=
=C2=A0</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"><div dir=3D"l=
tr"><div>Multiple transactions per connection.=C2=A0 I am asking WHY is tha=
t a feature.=C2=A0 when one can have multiple sessions, what=C2=A0is the di=
fference?=C2=A0 running multiple transactions in single=C2=A0or multiple se=
ssions means moving=C2=A0 part of transaction logic into the application sp=
ace. What do we gain here.....</div></div></blockquote><div>=C2=A0</div><di=
v>If I interpret=C2=A0&quot;Multiple transactions per connection&quot; corr=
ectly, they&#39;re a great way to emulate WITH HOLD cursors.</div><div><br>=
</div><div>For example:</div><div>1. In channel #1, open a Read Only cursor=
.=C2=A0 (Yes, this was long ago.)</div><div>2. Fetch a row.</div><div>3. Sw=
itch to channel #2, begin R/W txn, modify the table, commit.</div><div>4. S=
witch back to channel #1</div><div>5. Go to step 2.</div><div><br></div><di=
v>Not being an application=C2=A0developer anymore, I&#39;ve never needed to=
 use WITH HOLD cursors or wish for multiple channels in PG.</div><div><br><=
/div></div><span class=3D"gmail_signature_prefix">-- </span><br><div dir=3D=
"ltr" class=3D"gmail_signature"><div dir=3D"ltr">Death to &lt;Redacted&gt;,=
 and butter sauce.<div>Don&#39;t boil me, I&#39;m still alive.<br><div><div=
>&lt;Redacted&gt; lobster!</div></div></div></div></div></div>

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