Hi,
For example, an access path has 3 key fields in order: A, B and C.
Creation of this access path will result in 1 index. >>If a second access
path is then required with 2 key fields A and B then, on creation, will use
the existing index. So we >>have two access paths and only one index.
However, if the two access paths were created in reverse order then we'd
have 2 >>indexes with the associated overhead.
This is only true for access paths stored in DDS described logical file as
long as the first logical file has the same or a larger page size than the
newly created DDS described logical file. A DDS described logical file can
also share access path with an SQL index. An SQL index as a page size of 64K
per default while a DDS described logical file has only a page size of 8K
per default. If a DDS described logical file can share access path with a
SQL index, the DDS described logical file gets the larger access path size
of 64K inherited.
A SQL index on the other hand can only share access path with an other SQL
index and only if the keys are an exact match, that means the same key
fields in the same order. If the second SQL index has less key fields but in
the same order a second access path will be created and must be maintained.
Mit freundlichen Grüßen / Best regards
Birgitta Hauser
"Shoot for the moon, even if you miss, you'll land among the stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training them
and keeping them!"
-----Ursprüngliche Nachricht-----
Von: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von Keith McCully
Gesendet: Thursday, December 20, 2007 17:06
An: Midrange Systems Technical Discussion
Betreff: RE: SQL descending primary key
i wouldn't...i can use the table as is in RPG, etc. why add the
extra
overhead for an identical key??
I agree I wouldn't (see above). However, there should be no additional
overhead. The two indexes should share a common access path.
I think that it's the indexes are shared, where possible, between access
paths rather than the other way round.
For example, an access path has 3 key fields in order: A, B and C. Creation
of this access path will result in 1 index. If a second access path is then
required with 2 key fields A and B then, on creation, will use the existing
index. So we have two access paths and only one index. However, if the two
access paths were created in reverse order then we'd have 2 indexes with the
associated overhead.
Cheers,
Keith
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