Re: Repeatable Read Isolation Level "transaction start time"

On Tue, Sep 24, 2024 at 8:29 AM David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Monday, September 23, 2024, Wizard Brony <wizardbrony(at)gmail(dot)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:
>>
>> “UPDATE, DELETE, MERGE, SELECT FOR UPDATE, and SELECT FOR SHARE commands
>> 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.”
>>
>> 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 earlier
>> 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?

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