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Oracle

Troubleshooting Another Complex Performance Issue – Oracle direct path inserts and SEG$ contention

Here’s an updated presentation I first delivered at Hotsos Symposium 2015.

It’s about lots of concurrent PX direct path insert ant CTAS statements that, when clashing with another bug/problem, caused various gc buffer busy waits and enq: TX – allocate ITL entry contention. This got amplified thanks to running this concurrent workload on 4 RAC nodes:

When reviewing these slides, I see there’s quite a lot that needs to be said in addition to what’s on slides, so this might just mean a (Powerpoint) hacking session some day!

Which version of Oracle Linux should I pick for Oracle server product installations?

linux-tuxOracle certifies many of their latest products for installation on Oracle Linux 6 and 7, so I guess the obvious question is, which should you pick?

I tend to have a dual approach to this. I always use the latest versions of everything for my play kit, but I tend to be a little conservative for production deployments, preferring to use the OS version the product was developed against. I’ve noticed Oracle Cloud and some VM templates are still using Oracle Linux 6, which makes me think Oracle are being a little conservative too.

Application Performance Monitoring- First View

Working with test data is always fun and teaches those of us inside Oracle how best to use the new products that will be offered to benefit customers.  To me, it’s pretty straight forward and I didn’t first understand why it was necessary, but as I sit in on calls as we do performance testing of these great, new products, I understand why they need to direct so ma

Enterprise Manager at OOW 2015

Well, another Oracle Open World has bit the dust, and as is always the case, there was a lot of great material presented, both by Oracle employees and customers. To help you identify the material and get your hands on the presentations where possible, I’ve taken a stab at grouping all the material together into sections. These are the areas the presenters identified the material as covering, so if the title doesn’t seem to match that area blame the presenters. :)

Direct path and buffered reads again: compressed tables.

In the previous post on the decision between buffered and direct path reads I showed the decision is depended on the version. Up to and including version 11.2.0.2 the size of a segment needs to be five times small table threshold in order to be considered for direct path reads, and starting from 11.2.0.3 the database starts considering direct path reads starting from small table threshold. The lower limit just discussed is small table threshold or five times small table threshold with lower versions, upper limit is called “very large object threshold” (VLOT) and is five times the size of the buffercache, which is the threshold after which a table scan always is going via direct path.

Fedora 23 and Oracle 11gR2/12cR1

A few months ago I mentioned doing some Fedora 22 installations. At the time I did some pre-emptive installations on the Alpha release of Fedora 23 also.

Now the final release of Fedora 23 is out, I’ve run through the articles again to make sure things are all ship-shape.

The Eternal Newbie

It’s been over a decade since I first heard Tom Kyte talking about Project Marvel, which eventually became Application Express (APEX). Since then I’ve “used” just about every version of APEX. I use the term “used” very loosely, because I typically use APEX for a few days to get a job done, then never touch it again for months. By the time I come back, I pretty much have to start the learning process from the beginning again.

Wrong Results

Here’s a little gem in 12c that arrived in my email a few days ago: a query where the result depends on the SQL*Plus arraysize!

The email had a short description, and a script to create a small data set that would demonstrate the problem. I’m not going to show you the query, or the result set, but here’s a sample of the output from an SQL*Plus session after creating the data. This is, by the way, on a “single-user” system – there is no way that some other session is changing the data – especially after the opening “set transaction”:

The Hitchhiker’s Guide to the EXPLAIN PLAN Part 41: Why has my SQL execution plan changed?—A checklist

If the inputs to the CBO change, the plan can change. For example, changes to bind variables can cause the plan to change when it is hard parsed. Therefore one should never be surprised when plans change.(read more)

Oracle ACE program

What is the Oracle ACE program?

The Oracle ACE program is a community advocacy program for Oracle technology evangelists and enthusiasts, sponsored by and managed by Oracle Corporation.  As stated on the ACE overview page at “http://oracle.com/technetwork/community/oracle-ace”, it is both a network as well as a resource for everyone in the Oracle community.  It is not a certification program, and there is no course to study and no test to pass.  Rather, the ACE program is a recognition program by one’s colleagues and peers, and joining is a process of nomination, review, and acceptance.

Who are Oracle ACEs?