MIME-Version: 1.0
In-Reply-To: <9CEBFAC7-4372-4FF0-8124-FFFE834B03C6@gmail.com>
References: <9CEBFAC7-4372-4FF0-8124-FFFE834B03C6@gmail.com>
From: "David G. Johnston" <david.g.johnston@gmail.com>
Date: Tue, 24 Sep 2024 05:28:51 -0700
Message-ID: <CAKFQuwYvh02jtAAmybAPGC00k-AWiOqm3vT2Aj3m8dKLO+fugg@mail.gmail.com>
Subject: Re: Repeatable Read Isolation Level "transaction start time"
To: Wizard Brony <wizardbrony@gmail.com>
Cc: "pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
Content-Type: multipart/alternative; boundary="000000000000e485e20622dca58e"
Archived-At: <https://www.postgresql.org/message-id/CAKFQuwYvh02jtAAmybAPGC00k-AWiOqm3vT2Aj3m8dKLO%2Bfugg%40mail.gmail.com>
Precedence: bulk

--000000000000e485e20622dca58e
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Monday, September 23, 2024, Wizard Brony <wizardbrony@gmail.com> wrote:

> https://www.postgresql.org/docs/16/transaction-iso.html#
> XACT-REPEATABLE-READ
>
> The PostgreSQL documentation for the Repeatable Read Isolation Level
> states the following:
>
> =E2=80=9CUPDATE, DELETE, MERGE, SELECT FOR UPDATE, and SELECT FOR SHARE c=
ommands
> behave the same as SELECT in terms of searching for target rows: they wil=
l
> only find target rows that were committed as of the transaction start tim=
e.=E2=80=9D
>
> What is defined as the "transaction start time?" When I first read the
> statement, I interpreted it as the start of the transaction:
>
> BEGIN;
> SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
>
> But in my testing, I find that according to that statement, the
> transaction start time is actually "the start of the first
> non-transaction-control statement in the transaction" (as mentioned earli=
er
> in the section). Is my conclusion correct, or am I misunderstanding the
> documentation?
>
>
Probably, since indeed the transaction cannot start at begin because once
it does start it cannot be modified.

David J.

--000000000000e485e20622dca58e
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Monday, September 23, 2024, Wizard Brony &lt;<a href=3D"mailto:wizardbro=
ny@gmail.com">wizardbrony@gmail.com</a>&gt; wrote:<br><blockquote class=3D"=
gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-=
left:1ex"><a href=3D"https://www.postgresql.org/docs/16/transaction-iso.htm=
l#XACT-REPEATABLE-READ" target=3D"_blank">https://www.postgresql.org/<wbr>d=
ocs/16/transaction-iso.html#<wbr>XACT-REPEATABLE-READ</a><br>
<br>
The PostgreSQL documentation for the Repeatable Read Isolation Level states=
 the following:<br>
<br>
=E2=80=9CUPDATE, DELETE, MERGE, SELECT FOR UPDATE, and SELECT FOR SHARE com=
mands behave the same as SELECT in terms of searching for target rows: they=
 will only find target rows that were committed as of the transaction start=
 time.=E2=80=9D<br>
<br>
What is defined as the &quot;transaction start time?&quot; When I first rea=
d the statement, I interpreted it as the start of the transaction:<br>
<br>
BEGIN;<br>
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;<br>
<br>
But in my testing, I find that according to that statement, the transaction=
 start time is actually &quot;the start of the first non-transaction-contro=
l statement in the transaction&quot; (as mentioned earlier in the section).=
 Is my conclusion correct, or am I misunderstanding the documentation?<br>
<br>
</blockquote><div><br></div><div>Probably, since indeed the transaction can=
not start at begin because once it does start it cannot be modified.</div><=
div><br></div><div>David J.</div><div>=C2=A0</div>

--000000000000e485e20622dca58e--