New concurrency semantics in DB2
Many users access and change data in a relational database, the database manager
must allow users to make these changes while ensuring that data integrity is preserved.
In earlier DB2 versions, Cursor Stability (CS) isolation level prevented an application from reading any row that was changed
by other applications until the change was committed.
This causes Writers to block readers and Readers may block writers.
DB2 9.7 offers a new currently committed semantics to significantly improve concurrency.
With the enhancement, Writers do not block readers and Readers do not block writers.
Prior to DB2 9.7 |
Blocks -> |
Readers |
Writers |
Cursor Stability Isolation |
Readers |
NO |
MAY BE |
|
Writers |
YES |
YES |
In DB2 9.7 |
Blocks -> |
Readers |
Writers |
Cursor Stability Isolation |
Readers |
NO |
NO |
|
Writers |
NO |
YES |
The currently committed behavior is controlled by the database configuration parameter CUR_COMMIT. You can find out the setting of the parameter from TE, go to View > Configuration > DB Config.