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May 2014

Execution Plans

This is the index to a series of articles I’ve been writing for redgate, published on their AllThingsOracle site, about generating and interpreting execution plans.

When I started I didn’t really know how many parts it was going to end up as, I had thought maybe 5 or 6 but that was a wildly inaccurate estimate. It has finally ended at 14, and the last article will be published some time in the next week or so.

Costing Bug

It’s amazing how you can find little bugs (or anomalies) as soon as you start to look closely at how things work in Oracle. I started to write an article for All Things Oracle last night about execution plans with subqueries, so wrote a little script to generate some sample data, set up the first sample query, checked the execution plan, and stopped because the final cost didn’t make sense. Before going on I should point out that this probably doesn’t matter and probably wouldn’t cause a change in the execution plan if the calculation were corrected – but it is just an interesting indication of the odd things that can happen when sections of modular code are combined in an open-ended way. Here’s the query (running on 11.2.0.4) with execution plan:

Delete Histogram

Here’s a note which I drafted in Novemeber 2010, and then didn’t publish. I found it earlier on this morning while looking for another note I’d written about histograms so, even though it may not be something that people need so much these days, I thought: better late than never.

I’ve pointed out in the past that I’m not keen on seeing lots of histograms on a system and tend to delete them if I think they are not needed. Here’s an example of the type of code I use to delete a histogram.

Cloning Oracle RAC in 5 minutes

Chimpanzee playing with a laptop

 

How long does it take to create a clone of an Oracle RAC database? How complicated is it? How much experience does it take?

How about no experience and 5 minutes with a few mouse clicks?

The following video shows how to create a full RAC clone of a RAC source database in 5 minutes using Delphix. To see how Dephix links to the source database see the second video below.

 

Here is the RAC Delphix setup video, which similarly was finished in 5 minutes