Dirty reads, non-repeatable reads and phantom reads can occur.
This level allows a row changed by one transaction to be read
by another transaction before any changes in that row have been
committed (a "dirty read"). If any of the changes are rolled back,
the second transaction will have retrieved an invalid row.
Dirty reads are prevented; non-repeatable reads and phantom
reads can occur. This level only prohibits a transaction
from reading a row with uncommitted changes in it.
Dirty reads and non-repeatable reads are prevented; phantom
reads can occur. This level prohibits a transaction from
reading a row with uncommitted changes in it, and it also
prohibits the situation where one transaction reads a row,
a second transaction alters the row, and the first transaction
rereads the row, getting different values the second time
(a "non-repeatable read").
Dirty reads, non-repeatable reads and phantom reads are prevented.
This level includes the prohibitions in
REPEATABLE_READ
and further prohibits the
situation where one transaction reads all rows that satisfy
a WHERE condition, a second transaction inserts a row that
satisfies that WHERE condition, and the first transaction
rereads for the same condition, retrieving the additional
"phantom" row in the second read.
Dirty reads, non-repeatable reads and phantom reads can occur.
This level allows a row changed by one transaction to be read
by another transaction before any changes in that row have been
committed (a "dirty read"). If any of the changes are rolled back,
the second transaction will have retrieved an invalid row.
Dirty reads are prevented; non-repeatable reads and phantom
reads can occur. This level only prohibits a transaction
from reading a row with uncommitted changes in it.
Dirty reads and non-repeatable reads are prevented; phantom
reads can occur. This level prohibits a transaction from
reading a row with uncommitted changes in it, and it also
prohibits the situation where one transaction reads a row,
a second transaction alters the row, and the first transaction
rereads the row, getting different values the second time
(a "non-repeatable read").
Dirty reads, non-repeatable reads and phantom reads are prevented.
This level includes the prohibitions in
REPEATABLE_READ
and further prohibits the
situation where one transaction reads all rows that satisfy
a WHERE condition, a second transaction inserts a row that
satisfies that WHERE condition, and the first transaction
rereads for the same condition, retrieving the additional
"phantom" row in the second read.
