User Guide

SAP AG November 2002
Isolation Level 15
The following rules apply if isolation level [Page 139] 15 is specified:
For all SQL statements, the behavior described for isolation level 1 or 10 [Page 117] also
applies for isolation level 15: The only difference is that, with isolation level 15,
are requested for all the tables addressed by the SQL statement before
processing starts. When the SQL statement generates a result table that is not physically
stored, these locks are not released until the end of the transaction or until the result table is
closed. Otherwise, they are released immediately after the SQL statement has been
processed.
shared locks
[Page 114]
When rows are inserted, updated or deleted, implicit
are assigned
to the
for the rows concerned. These cannot be released until the end
of the transaction.
exclusive locks [Page
115]
transaction [Page
152]
Isolation Level 2 or 20
If isolation level [Page 139] 2 or 20 (repeatable) is specified, shared locks [Page 114] are
requested for all the tables addressed by the SQL statement before processing starts.
When the SQL statement generates a result table that is not physically stored, these locks are
not released until the end of the transaction or until the result table is closed. Otherwise, they
are released immediately after the SQL statement has been processed. This table shared
lock is not assigned to the
in the case of SQL statements in which just
one table row is processed that is determined by
or
by CURRENT OF <result_table_name>.
transaction [Page
152]
key specifications [See SAP DB Library]
In addition, an implicit shared lock is assigned to the transaction for each row read while an
SQL statement is being processed. These locks can only be released with the UNLOCK
statement [See SAP DB Library] or by ending the transaction.
When rows are inserted, updated or deleted,
are assigned
implicitly to the transaction for the rows concerned. These cannot be released until the end of
the transaction.
exclusive locks [Page
115]
Isolation Level 3 or 30
If isolation level [Page 139] 3 or 30 (serializable) is specified, a table shared lock [Page 114]
is implicitly assigned to the transaction [Page 152] for every table addressed by an SQL
statement.
These shared locks cannot be released until the end of the transaction. This table shared lock
is not assigned to the transaction in the case of SQL statements in which just one table row is
processed that is determined by key specifications [See SAP DB Library]
or by CURRENT OF
<result_table_name>.
When rows are inserted, updated or deleted,
115 are assigned
implicitly to the transaction for the rows concerned. These cannot be released until the end of
the transaction.
exclusive locks [Page
]
User Manual: SAP DB 118