Database Administrator Guide > Database Administrator Guide > Understanding Multiversion Concurrency Control > What Data Does the User See?
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What Data Does the User See?
The data the user sees when the lock level is MVCC depends on the isolation level setting.
1. User1 : SELECT * FROM x1;
2. User2 : INSERT INTO x2 VALUES(100);
3. User2 : COMMIT;
4. User1 : SELECT * FROM x2;
Isolation Level
Read Consistency Level
Snapshot Corresponds To
SELECT x2 By User1 at Line 4
Serializable
Transaction
Start of transaction Line 1
Does not see new value
Read Committed
Statement
Start of statement Line 4
Does see new value
Note:  With traditional locking (no MVCC), User1 would see the new value of the data at Line 4 (Transaction 3).
Last modified date: 08/14/2024