A Network54 Essbase board user asked a question today that I’ve heard a few times without ever being sure of the answer:
“If the MDX report run after query tracking is enabled returns no data… ….does it still aggregate?”
In other words, if you turn on query tracking in ASO and then run queries, but those queries only return #Missing instead of finding some data, will the queries still affect the aggregate views that Essbase chooses?
I’ve been working on tuning aggregate views with a test copy of a large ASO cube to which I added some additional dimensions. Tuning aggregate views can be tricky, because aggregate views make query performance heavily dependent on the exact combination of levels being queried. And there’s always some user that comes along with an unusual query that happens to hit a combination of levels that performs particularly poorly. So when I handed the system over for front-end certification by users, I enabled query logging. By parsing the log for “worst case” query times, I could proactively monitor and then investigate any particularly nasty cases the users encountered. Unfortunately, I was being a little bit too smart for my own good.
This post is a quick follow-on to my last, inspired by the same piece of client work. Fair warning: it’s only going to make sense if you are already somewhat familiar with aggregate views and view definition scripts (.csc). If you’re not already familiar with the concepts but want to read this anyway, I’d refer you to a presentation given at Kscope11 as an excellent (ahem) primer on the topic (free associate membership of ODTUG required).
But in summary: Many people maintaining larger or complex ASO cubes have developed very carefully crafted sets of aggregate views to optimize query performance. They also know that, unfortunately, some structural changes can invalidate those view definitions – adding levels to stored dimensions and adding new stored dimensions to name two. This can necessitate a lot of painstaking, trial-and-error optimization to generate a new set of aggregate views that provide equivalent performance to the original set.
In the course of adding a new dimension to an existing cube, I realized that there was a straightforward way to preserve the validity of my existing set of aggregate views.
A long gap since my last blog entry – for which I’m going to mostly blame Kscope…
I’ve mentioned before that I really enjoy the Unix tools and am working at becoming more competent with them. In this post, I’m going to explain why adding a new dimension to an ASO cube while retaining existing data is slightly harder than doing the same to a BSO cube, and then show how I used a very simple script (ksh, but these are such basic commands that I’m sure it can be translated easily if not used exactly as is) to modify native export files and solve the problem.
Essbase is Wrong
Once or twice I’ve got stuck troubleshooting an ASO query or MDX member formula, only to discover – after some head-scratching – that Essbase and I disagree about the appropriate value of a metadata property on an implicitly shared member. Whether the (very strange) behavior described below is by design I don’t know, but since ASO and BSO do not behave the same way and I can’t find any documentation describing a difference in this area, I have to suspect not. Continue reading