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help / color / mirror / Atom feedFrom: Greg Sabino Mullane <[email protected]>
To: Christophe Pettus <[email protected]>
Cc: Ron Johnson <[email protected]>
Cc: pgsql-generallists.postgresql.org <[email protected]>
Subject: Re: Repeatable Read Isolation Level "transaction start time"
Date: Wed, 25 Sep 2024 17:50:06 -0400
Message-ID: <CAKAnmm+pudxS+6P8QWH-hf9sUcUN8LuY2tQpc+8_-Gnwi2WNRQ@mail.gmail.com> (raw)
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On Wed, Sep 25, 2024 at 4:54 PM Christophe Pettus <[email protected]> wrote:
> On Sep 25, 2024, at 13:49, Greg Sabino Mullane <[email protected]> wrote:
> > BEGIN ISOLATION MODE REPEATABLE READ SNAPSHOT NOW;
>
> This might well be a failure of imagination on my part, but when would it
> pragmatically matter that the snapshot is taken at the first statement as
> opposed to at BEGIN?
I could imagine lots of cases where you know something is about to happen
(say, a major delete), and you want to get a snapshot of the database as it
existed just before that point. Many people will (quite understandably)
assume that a BEGIN ISOLATION MODE <non read committed>; command would do
just that, and be quite surprised to find that when they actually query the
table in that first process, the rows are not there.
It's certainly a non-intuitive behavior. I understand why we do it this
way, but perhaps this warrants a stronger warning in the docs at least?
It's too late in the day for me to tackle that now, but I'll throw it out
there.
Cheers,
Greg
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To: [email protected]
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Subject: Re: Repeatable Read Isolation Level "transaction start time"
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