Re: System i DDS Files

SQL view will NOT impact performance (there is no keyed access path being
maintained). Think of it as a non-keyed LF.
The only thing worth mentioning here is that if you query an LF, DB2 will
route your query to the older CQE engine. If you query an SQL view, your
query will take the new SQE engine (provided no other SQE restriction is
hit).

When looking at it with SQL perspective, SQL index (aka keyed LF) only
purpose in life is to improve performance of your queries. When you're doing
inserts/updates/deletes DB2 has to maintain the keyed access path (index) in
real time, but you get a pay-off when you run your SELECTs (read access). So
there is a slight trade-off, depending on the prevalent access your
application performs (writes vs reads). My experience is that most
applications do several orders of magnitude more reads than writes.
Fact is, without a proper indexing strategy and with database of any
appreciable size, your SELECTs will perform poorly.

I am not clear about your reference to index rebuilds. DB2 doesn't perform
index rebuilds on any regular basis. They only happen in exceptional
circumstances, so I'd advise not to worry about them needlessly. DB2 for i
takes care of you in this and many other respects (i.e. storage management).

BTW, having 'too many' indexes is an outdated notion nowadays. The new SQE
engine will work well regardless of the number of indexes you have (i.e.
there is not query optimizer timeout any longer). Just make sure your
queries run in the newer SQE engine (don't query LFs directly, don't use
*LANGIDSHR on V5R4 (ok on V6R1) etc.)

Hth, Elvis

Celebrating 11-Years of SQL Performance Excellence on IBM i, i5/OS and
OS/400
www.centerfieldtechnology.com


-----Original Message-----
Subject: [SystemiDotNet] System i DDS Files


Many thanks for the information from you guys.
Is there a difference in .NET between using an SQL view or a logical DDS
file?

This may not be the right list to ask this question, but it does relate to
my .NET project.
We always restrict the number of logicals over a physical file because it
will effect the performance (index rebuilds). So, will an SQL View impact
the performance of a physical file like a logical file does?