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Re: Repeatable Read Isolation Level "transaction start time" - Mailing list pgsql-general

From Ron Johnson
Subject Re: Repeatable Read Isolation Level "transaction start time"
Date
Msg-id CANzqJaBjwtzLg_bZHkokUJbtA8gy6RpHjirfdBH9OJGfn5=tmw@mail.gmail.com
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In response to Re: Repeatable Read Isolation Level "transaction start time"  (Adrian Klaver <adrian.klaver@aklaver.com>)
Responses Re: Repeatable Read Isolation Level "transaction start time"
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On Wed, Sep 25, 2024 at 1:45 PM Adrian Klaver <adrian.klaver@aklaver.com> wrote:


On 9/25/24 10:22 AM, Greg Sabino Mullane wrote:
> On Tue, Sep 24, 2024 at 10:28 AM Tom Lane <tgl@sss.pgh.pa.us
> <mailto:tgl@sss.pgh.pa.us>> wrote:
>
>     It's even looser than that, really: it's the first statement that
>     requires an MVCC snapshot.
>
>
> Hm....so why does "SELECT 1;" work as a transaction start marker then,
> as opposed to "SHOW work_mem;", which does not? Do we simply consider
> anything with a SELECT as needing a snapshot?


SELECT some_func();

Where some_func() does something that requires a snapshot.


But why does "SELECT 1;" need a snapshot?  Heck, why does "SELECT <immutable>;" need a snapshot? 

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