On Thu, Mar 2, 2023 at 01:55:31PM +0000, PG Doc comments form wrote: > The following documentation comment has been logged on the website: > 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.
Well, the point is that the application is _not_ retrieving a value and setting is +100, but rather having the SQL add 100, which is kind of the point. I don't think a tutorial should get into more details than that. -- Bruce Momjian <br...@momjian.us> https://momjian.us EDB https://enterprisedb.com Embrace your flaws. They make you human, rather than perfect, which you will never be.
