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Restrictions on parallel DML

原创 Linux操作系统 作者:v_fantasy 时间:2009-03-28 18:51:59 0 删除 编辑
parallel DML (including direct-path INSERT):
  • Intra-partition parallelism for UPDATE, MERGE, and DELETE operations require that the COMPATIBLE initialization parameter be set to 9.2 or greater.
  • INSERT, UPDATE, MERGE, and DELETE operations on nonpartitioned tables are not parallelized if there is a bitmap index on the table. If the table is partitioned and there is a bitmap index on the table, the degree of parallelism will be restricted to at most the number of partitions accessed.
  • A transaction can contain multiple parallel DML statements that modify different tables, but after a parallel DML statement modifies a table, no subsequent serial or parallel statement (DML or query) can access the same table again in that transaction.
    • This restriction also exists after a serial direct-path INSERT statement: no subsequent SQL statement (DML or query) can access the modified table during that transaction.
    • Queries that access the same table are allowed before a parallel DML or direct-path INSERT statement, but not after.
    • Any serial or parallel statements attempting to access a table that has already been modified by a parallel UPDATE, DELETE, or MERGE, or a direct-path INSERT during the same transaction are rejected with an error message.
  • If the initialization parameter ROW_LOCKING is set to intent, then inserts, updates, merges, and deletes are not parallelized (regardless of the serializable mode).
  • Parallel DML operations cannot be done on tables with triggers.
  • Replication functionality is not supported for parallel DML.
  • Parallel DML cannot occur in the presence of certain constraints: self-referential integrity, delete cascade, and deferred integrity. In addition, for direct-path INSERT, there is no support for any referential integrity.
  • Parallel DML can be done on tables with object columns provided you are not touching the object columns.
  • Parallel DML can be done on tables with LOB columns provided the table is partitioned. However, intra-partition parallelism is not supported.
  • A transaction involved in a parallel DML operation cannot be or become a distributed transaction.
  • Clustered tables are not supported.

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