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parallel dml & referential integrity constraints

原创 Linux操作系统 作者:v_fantasy 时间:2009-03-30 13:23:10 0 删除 编辑
lists all of the parallel operations that are possible on tables that are involved in referential integrity constraints. Table 21-1 Referential Integrity Restrictions 
DML Statement Issued on Parent Issued on Child Self-Referential

INSERT

(Not applicable)

Not parallelized

Not parallelized

MERGE

(Not applicable)

Not parallelized

Not parallelized

UPDATE No Action

Supported

Supported

Not parallelized

DELETE No Action

Supported

Supported

Not parallelized

DELETE Cascade

Not parallelized

(Not applicable)

Not parallelized

Delete Cascade

Delete on tables having a foreign key with delete cascade is not parallelized because parallel execution servers will try to delete rows from multiple partitions (parent and child tables).

Self-Referential Integrity

DML on tables with self-referential integrity constraints is not parallelized if the referenced keys (primary keys) are involved. For DML on all other columns, parallelism is possible.

Deferrable Integrity Constraints

If any deferrable constraints apply to the table being operated on, the DML operation will not be parallelized.

Trigger Restrictions

A DML operation will not be parallelized if the affected tables contain enabled triggers that may get fired as a result of the statement. This implies that DML statements on tables that are being replicated will not be parallelized.

Relevant triggers must be disabled in order to parallelize DML on the table. Note that, if you enable or disable triggers, the dependent shared cursors are invalidated.

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