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Correlated subselects are often resource-intensive because the subselect is evaluated for each qualifying value in the outer select. When compared to JOIN, the WHERE predicate is evaluated in Stage 1, thus reducing the rows passed to Stage 2 and the correlated predicate is evaluated in Stage 2.

Cursor Stability (CS), Repeatable Read (RR), Read Stability (RS), Uncommitted Read (UR). Cursor stability holds locks as long the cursor is position on the row. Repeatable read holds locks on all the rows on both qualifying and non-qualifying rows. Read stability holds locks only on qualifying rows ...

DB2 uses the LOCKSIZE parameter defined in the CREATE TABLESPACE statement.

In addition to the above, you can specify isolation level in the SQL statement eg. SELECT .... FROM ....WITH UR;

No, the lock is not released until commit.

If a region that is abending is in a DLI call, will kill the control region. The control region will abend with U113. Look in the IMS messages for U113 for more information.