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Answer Posted / pandurangan
DB2 ensures concurrency through ISOLATION levels, which
determines how data that is accessed or modified by one
transaction is isolated from other transaction.
There are 4 levels of isolation
1) Repeatable Read - if a transaction scans 1000 rows to
retrieve 20 rows, lock is acquired and held on all 1000 rows
until the transaction is complete.
2) Read Stability - If 10 rows are retrieved then lock will
be on 10 rows only till the completion of transaction.
3) Cursor Stability - Only locks the row that is referenced
by a cursor that was declared and owned by the transaction.
4) Uncommitted Read - Its just like read, since you haven't
committed you can see others making changes to it while you
are still on it.
For more details go to http://db2guide.blogspot.ie/
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