Logging and Buffering - Transaction Processing - page 51

3.4 Logging for the Read-Write and Key-Range Models

In the following we list the physiological log records for various actions in the
read-write and key-range transaction models. In the log records below, T denotes a
transaction identifier, and n is the LSN assignedtothelogrecord.
The begin-transaction action B of transaction T

is logged with the begin-

transaction log record

n Wh T; B i : (3.2)

The commitment or completion of rollback C of transaction T is logged with the
commit log record

n Wh T; C i : (3.3)

The abort A of transaction T is logged with the abort log record

n Wh T; A i : (3.4)

The action SŒP of setting savepoint P in transaction T is logged with the set-
savepoint log record

n Wh T; SŒP ; n 0 i ; (3.5)

where n 0 is the U NDO -N EXT -LSN of T when the action is being performed. The U NDO -
N EXT -LSN value is needed in order to correctly update U NDO -N EXT -LSN .T / when a
partial rollback to savepoint P has been performed.
The action AŒP of beginning partial rollback to savepoint P in transaction T is
logged with the begin-rollback-to-savepoint log record

n Wh T; AŒP i : (3.6)

The action CŒP of completing partial rollback to savepoint P in transaction T
is logged with the complete-rollback-to-savepoint log record

n Wh T; C ŒP i : (3.7)

The log record for a forward-rolling update action (W , I , D) by transaction T
contains the name and arguments of the action, as well as the U NDO -N EXT -LSN
value n 0 set from U NDO -N EXT -LSN .T / when the action is being performed; the value
n 0 is needed for updating U NDO -N EXT -LSN .T / after possibly undoing the logged
action in a partial or total rollback.