OS/400 V5R4升级-INGNORE_DERIVED_INDEXES参数设置原因（SQE）

OS/400 V5R4升级-INGNORE_DERIVED_INDEXES参数设置原因

 

Sure, but DDS described logical files with select/omit clauses can only be
used by the CQE (Classic Query Engine).
In this way all queries executed against physical files that have DDS
described logical files with select/omit clauses, are rerouted to the old
CQE.

The only way to avoid the rerouting is to change the the option
INGNORE_DERIVED_INDEXES in the QAQQINI-File from *NO to *YES.

Executing Queries with the SQE will in most cases be much more performant
than executing the same query with the CQE.

If an access path is missed, the existing logical file can be deleted, an
index with the appropriate key fields created and the logical file
recreated. In this way, the access path stored in the SQL index can be used
by the SQE and the DDS described logical file will share the access path
with the SQL index. That means there is only a single access path that must
be actualized. BTW a DDS described logical file can share access path with a
SQL index, but a SQL index cannot share access paths with DDS a described
logical file, because of the larger page size of the SQL index (64K versus
8K for DDS files)

 

With 6.1. the SQE is terminated and with the new derived indexes most
logical files with select/omit clauses can be replaced.
In this way it should be possible to execute ALL queries with the SQE.
That's why the default value for IGNORE_DERIVED_INDEXES was changed to *YES.

 

Mit freundlichen Grü en / Best regards

 

译文：

 

   用cqe只能作为用DDS描述的lf的数据库引擎的。所有没有用上述定义的所有queries将会返回到使用cqe的路径上。为避免这种返回cqe路径的唯一方法就是设置QAQQINI表中IGNORE_DERIVED_INDEXES参数，由‘*NO’改为‘*YES’.

 

   在大多数情况下，用执行sqe为引擎的queries会比使用CQE为引擎的queries性能高。如果因为一个存在的逻辑文件被删除一条访问路径丢失了，在重新建立这个逻辑文件的同时，一个使用相关键值的索引也被创建。在这种情况下，在SQL索引中的这条访问路径能被SQE引擎使用，并且用SQL索引用DDS描述创建的逻辑文件能够共享这条访问路径。这就意味着只有单一的访问路径必须创建。顺便说说，一个用DDS描述的逻辑文件能使用SQL索引共享其访问路径，但是用一个DDS描述的逻辑文件不能共享SQL索引的访问路径，因为SQL索引使用64k较大的页面（DDS文件只有8k）。

 

使用6.1版，sqe肯定作为检索引擎，并且使用新的驱动索引，大多数使用select/omit clauses的逻辑文件能被替换。用这种方法，这些clauses应该可能用sqe执行所有的queries。这就是为什么把IGNORE_DERIVED_INDEXES 参数设置为 *YES的原因。