Q about read committed in Oracle...
От | Vadim Mikheev |
---|---|
Тема | Q about read committed in Oracle... |
Дата | |
Msg-id | 35AB3B2E.F3C19FC9@krs.ru обсуждение исходный текст |
Список | pgsql-hackers |
This is said in Oracle7 Server Concepts Manual, Data Concurrency, Additional Considerations for Serializable Isolation: --- Both read committed and serializable transactions use row-level locking, and both will wait if they try to change a row updated by an uncommitted concurrent transaction. The second transaction that tries to update a given row waits for the other transaction to commit or rollback and release its lock. If that other transaction rolls back, the waiting transaction (regardless of its isolation mode) can proceed to change the previously locked row, as if the other transaction had not existed. However, read committed and serializable transactions behave differently if the other (blocking) transaction commits. When the other transaction commits and releases its locks, a read committed transaction will proceed with its intended update... ^^^^^^^^ --- What does this mean? Will Oracle update this row (just updated by other Xaction)? In any case or only if qualification is ok for this row now (qual was ok for unchanged version of row but could be changed by concurrent Xaction)? Could someone run in Oracle test below? 1. CREATE TABLE test (x integer, y integer) 2. INSERT INTO test VALUES (1, 1); INSERT INTO test VALUES (1, 2); INSERT INTO test VALUES (3, 2); 3. run two session T1 and T2 (in read committed mode) 4. in session T2 run UPDATE test SET x = 1, y = 2 WHERE x <> 1 OR y <> 2; 5. in session T1 run UPDATE test SET y = 3 WHERE x = 1; 6. in session T2 run COMMIT; 7. in session T1 run SELECT * FROM test; -- results? 8. in session T1 run COMMIT; 9. now in session T2 run UPDATE test SET x = 2; 10. in session T1 run UPDATE test SET y = 4 WHERE x = 1; 11. in session T2 run COMMIT; 12. in session T1 run SELECT * FROM test; -- results? TIA, Vadim
В списке pgsql-hackers по дате отправления: