SERIALIZABLE (6) |
In this isolation level, problems concerning concurrency (e.g.
dirty read, non-repeatable read, phantom read, etc.) do not
occur. |
REPEATABLE READ CLASS with REPEATABLE READ INSTANCES (5) |
Another transaction T2 cannot update the schema of table A while
transaction T1 is viewing table A.
Transaction T1 may experience phantom read for the record R that was
inserted by another transaction T2 when it is repeatedly retrieving a
specific record. |
REPEATABLE READ CLASS with READ COMMITTED INSTANCES (or CURSOR STABILITY) (4) |
Another transaction T2 cannot update the schema of table A while
transaction T1 is viewing table A.
Transaction T1 may experience R read (non-repeatable read) that was
updated and committed by another transaction T2 when it is repeatedly
retrieving the record R. |
REPEATABLE READ CLASS with READ UNCOMMITTED INSTANCES (3) |
Default isolation level. Another transaction T2 cannot update
the schema of table A while transaction T1 is viewing table A.
Transaction T1 may experience R' read (dirty read) for the record that
was updated but not committed by another transaction T2. |
READ COMMITTED CLASS with READ COMMITTED INSTANCES (2) |
Transaction T1 may experience A' read (non-repeatable read) for
the table that was updated and committed by another transaction T2
while it is viewing table A repeatedly. Transaction T1 may experience
R' read (non-repeatable read) for the record that was updated and
committed by another transaction T2 while it is retrieving the record
R repeatedly. |
READ COMMITTED CLASS with READ UNCOMMITTED INSTANCES (1) |
Transaction T1 may experience A' read (non-repeatable read) for
the table that was updated and committed by another transaction T2
while it is repeatedly viewing table A. Transaction T1 may experience
R' read (dirty read) for the record that was updated but not committed
by another transaction T2. |