Re: DB View performance

Aside from Visual Explain I have 2 ideas:

1. try to rebuild your indexes after the view is recreated - I had such a strange experience lately with a "coupled" view/index pair

2. does "myfield" contain NULLs? Or is "myfield" part of a LEFT JOINed table/view? If not, try COUNT(*) as it does not have to inspect every value of "myfield" it is normally faster in this particular case

HTH
Daniel

Am 27.05.2026 um 20:09 schrieb Vern Hamberg via MIDRANGE-L <midrange-l@xxxxxxxxxxxxxxxxxx>:

In addition to Rob's suggestion, have you run Visual Explain over both the original and the new views? Something about this makes me wonder about a table scan, although the system should know how many rows are in a table without doing a table scan. You might do a table scan on the old view, as well.

I also wonder about the plan cache - the old view has been used a lot, and optimization has found the best plan. The new view might need to be run many times to get better performance. And Visual Explain would help with getting things better sooner.

Also, if you can, run VE in an environment that has substantially the same environment - table sizes, memory, things like that.

*Regards*

*Vern Hamberg*

IBM Champion 2025 <cid:part1.PkYYiEO0.NE0lbl8t@centurylink.net> CAAC (COMMON Americas Advisory Council) IBM Influencer 2023

On 5/27/2026 12:47 PM, Rob Berendt wrote:
Did you use the tool to retrieve the SQL source of your old view and
compare it to the one you recreated without the new column?

On Wed, May 27, 2026 at 1:42 PM Greg Wilburn <
gwilburn@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

I have a relatively complicated database view that references other
views. Back in 2020, I was able to create some indexes to improve
performance when this view was used.

Without going into a lot of detail, I added a column to the view to simply
count the lines in the primary table (the view already groups results). I
did this generating the DDL from ACS Schemas tool. Using run sql scripts,
I did a "create or replace view" after adding the column. This change
killed the performance, so I removed the new column and ran "create or
replace view" again.

Now to the odd part... the performance was still horrible. I didn't know
what to do, so I restored the view from our cloud backup - this fixed the
performance issue.

My question is why? What is happening behind the scene that I'm not
considering?
I honestly can't imagine that adding a "count(myfield) as mynewfield"
column would dramatically affect the performance.

Greg
[Logo]<https://www.totalbizfulfillment.com/> Greg Wilburn
Director of IT
301.895.3792 ext. 1231
301.895.3895 direct
gwilburn@xxxxxxxxxxxxxxxxxxxxxxx<mailto:gwilburn@xxxxxxxxxxxxxxxxxxxxxxx>
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Grantsville, MD 21536
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