merge

I’m sure there will be a slew of post-Kscope wrap up posts coming out into the blogosphere, so in lieu of that, and the the fact that I’m just stuck in an airport waiting for a flight, I’ll offer something slightly more technical. I did a post a while back about a curious error “unable to get a stable set of rows” when using MERGE. Here is another variant which can occur when you allow rows to physically move during a MERGE.

“How is that possible?” I hear you ask. Easy. All we need is partitioned table with ENABLE ROW MOVEMENT.

Just a quick blog post on MERGE and the “unable to get a stable set of rows” error that often bamboozles people. This is actually just the script output from a pre-existing YouTube video (see below) that I’ve already done on this topic, but I had a few requests for the SQL example end-to-end, so here it is.

Imagine the AskTOM team had a simple table defining the two core members, Chris Saxon and myself. But in the style of my true Aussie laziness, I was very slack about checking the quality of the data I inserted.

As you can tell, I have no idea on a name for what I am about to describe. So let me start from the beginning, and set the scene for an idea I have to utilize a cool new 18c feature.

Often in a transactional-style system the busiest table (let us call it SALES for the sake of this discussion) is also

• the biggest table, after all, it has all of our sales in it,
• the most demanded for table, in that, almost every query in our application wants to access it in some way shape or form.

This is in effect the database version of the Pareto Principle. Everyone wants a slice of that SALES “pie”, and the piece of that pie that is in most demand is typically the most recent data. Your application may have pages that will be showing:

One of the cool things in 18c is the ability to merge partitions without causing a service interruption.  Here’s a video demonstration of that in action:

This is just an accompanying blog post to let you grab the scripts for the demo so that you can try this yourself on livesql.oracle.com, or any of the Oracle Cloud services that will be running 18c in the near future.