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From: Ron Johnson <ronljohnsonjr@gmail.com>
Date: Tue, 24 Sep 2024 08:59:01 -0400
Message-ID: <CANzqJaC0Puj0WnnjQ2K2qy1MQJY4O8QP5uJbNoqeQrhfdgJ8Xg@mail.gmail.com>
Subject: Re: Repeatable Read Isolation Level "transaction start time"
To: "pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
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On Tue, Sep 24, 2024 at 8:29=E2=80=AFAM David G. Johnston <
david.g.johnston@gmail.com> wrote:

> 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 =
commands
>> behave the same as SELECT in terms of searching for target rows: they wi=
ll
>> only find target rows that were committed as of the transaction start ti=
me.=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 earl=
ier
>> 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.
>

Huh?

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

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<div dir=3D"ltr"><div dir=3D"ltr">On Tue, Sep 24, 2024 at 8:29=E2=80=AFAM D=
avid G. Johnston &lt;<a href=3D"mailto:david.g.johnston@gmail.com">david.g.=
johnston@gmail.com</a>&gt; wrote:<br></div><div class=3D"gmail_quote"><bloc=
kquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:=
1px solid rgb(204,204,204);padding-left:1ex">On Monday, September 23, 2024,=
 Wizard Brony &lt;<a href=3D"mailto:wizardbrony@gmail.com" target=3D"_blank=
">wizardbrony@gmail.com</a>&gt; wrote:<br><blockquote class=3D"gmail_quote"=
 style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);p=
adding-left:1ex"><a href=3D"https://www.postgresql.org/docs/16/transaction-=
iso.html#XACT-REPEATABLE-READ" target=3D"_blank">https://www.postgresql.org=
/docs/16/transaction-iso.html#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><=
/blockquote><div>=C2=A0</div></div>Huh?<br clear=3D"all"><div><br></div><sp=
an 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 sa=
uce.<div>Don&#39;t boil me, I&#39;m still alive.<br><div><div>&lt;Redacted&=
gt; crustacean!</div></div></div></div></div></div>

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