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From: Wizard Brony <[email protected]>
To: [email protected]
Subject: Repeatable Read Isolation Level "transaction start time"
Date: Mon, 23 Sep 2024 11:15:20 -0400
Message-ID: <[email protected]> (raw)

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?

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