The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/15/tutorial-transactions.html
Description:
Hi,
I just discovered that by default, transactions are not entirely isolated. I
think that the tutorial should mention this.
The tutorial gives the example of a bank account, where you make two
commands, one to increase the balance and one to decrease the balance,
explaining why you need a transaction. The example, in which the command is
"UPDATE accounts SET balance = balance - 100.00 WHERE name = 'Alice'", would
indeed be correct with the default transaction isolation. However, if the
transaction included getting the balance by a program, adding 100 to it, and
then setting the balance, consistency would not always be kept, since
another transaction could have modified the balance in between. By just
reading the tutorial, the reader would have no idea that this may happen.
I think that a notice saying that for absolute transaction isolation you
should set the default transaction isolation to serializable, and be
prepared to have transactions fail, and referring to the more details
document, would help users prevent consistency bugs.
Thanks,
Noam