RE: Finding a hole in a sequence using SQL vs native I/O -- MIDRANGE-L

Thanks for taking the time to gather that information Joe.

Charles Wilt
Software Engineer
CINTAS Corporation - IT 92B
513.701.1307

wiltc@xxxxxxxxxx

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-
bounces@xxxxxxxxxxxx] On Behalf Of Joe Pluta
Sent: Wednesday, April 16, 2008 12:53 PM
To: Midrange Systems Technical Discussion
Subject: Finding a hole in a sequence using SQL vs native I/O

Wilt, Charles wrote:

You're correct given the way you've coded the SQL.

However, my conclusions' were based on Michael's SQL. While not 100%,

I'm pretty sure his SQL won't

need the temp table or read the index more than once behind the scenes.

But testing would tell us for sure.

Testing confirms for me that SQL is indeed faster if the first "hole" is
somewhere out past 60-70% of the way into the file. This is consistent
with the idea that the more I/O you do, the more likely SQL is to
process better.

Interestingly, both SQLs perform about the same way. On my machine, it
takes about 7 seconds to find a hole halfway into an 900,000 record file
(using either SQL - the difference seems negligible, but I haven't done
a bunch of testing). It takes about 5.7 seconds for the read. At
600,000 it takes 8 seconds for the SQL, and about 9.7 for the read. At
the end, it takes 9 seconds for the SQL, and nearly 14 for the read.

How would this be faster than just reading 500,000 records
sequentially? There is no magic in SQL, except that it doesn't need to
bounce back and forth between the HLL and the SLIC. But I can't see

how

that will help this particular problem.

My conclusions assume Michaels' SQL will read through the index once.

Thus, the SQL would be faster....

What's interesting is the consistency in the SQL approach. It seems to
indicate that is a temporary index being built. Even if the 10th record
is not found, the SQL still takes around 7 seconds. And as you can
guess, with the read technique, it takes milliseconds. My conclusion is
that if your holes are interspersed throughout your file, native I/O is
your answer. If your holes are consistently at the end of the sequence,
go with SQL.

Joe

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