These days I improved my knowledge about Isolation Level of transactions.
In particular, i had problem to understand well the difference between Read Committed and Repeatable Read.
I've read this fantastic article, and I understand all about dirty-reads, non-repeatable read and phantoms read but i don't understand what happen with multiple transactions in update.
Example:
Table: "Test" (Field: ID_REC - Data)
Transaction A:
set transaction isolation level read committed;
begin transaction
update test
set DATA = 't1'
where ID_REC = 1
waitfor delay '00:00:20'
commit transaction
Transaction B: (the same but with another record)
set transaction isolation level read committed;
begin transaction
update test
set DATA = 't2'
where ID_REC = 2
commit transaction
I execute both transactions in two seconds. Second transaction doesn't start until first one is finished. And also i can't execute query (select * from test).
So: why happen this? Transactions works on different rows... and about this case, what is the difference between Read Committed and Repeatable Read?
