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.
