Oracle Scratchpad

August 19, 2012

Compression Units – 5

Filed under: CBO,Exadata,HCC,Indexing,Oracle — Jonathan Lewis @ 6:02 pm BST Aug 19,2012

The Enkitec Extreme Exadata Expo (E4) event is over, but I still have plenty to say about the technology. The event was a great success, with plenty of interesting speakers and presentations. As I said in a previous note, I was particularly keen to hear  Frits Hoogland’s comments  on Exadata and OLTP, Richard Foote on Indexes, and Maria Colgan’s comments on how Oracle is making changes to the optimizer to understand Exadata a little better.

All three presentations were interesting – but Maria’s was possiby the most important (and entertaining). In particular she told us about two patches for, one current and one that is yet to be released (unfortunately I forgot to take  note of the patch numbers – ed: but they’ve been supplied by readers’ comment below).

August 7, 2012

Compression Units – 4

Filed under: Exadata,HCC,Oracle — Jonathan Lewis @ 5:24 pm BST Aug 7,2012

Following up a suggestion from Kerry Osborne that I show how I arrived at the observation I made in an earlier posting about the size of a compression unit, here’s a short note to show you what I did. It really isn’t rocket science (that’s just a quick nod to NASA and Curiosity – the latest Mars rover).

Step 1: you can access rows by rowid in Oracle, so what happens when you try to analyze rowids on Exadata for a table using HCC ? I created a table with the option “compress for archive high” and then ran the following query:

July 27, 2012

Compression Units – 3

Filed under: Exadata,HCC,Oracle — Jonathan Lewis @ 5:08 pm BST Jul 27,2012

For those who have read the previous posting of how I engineered an Exadata disaster and want to reproduce it, here’s the script I used to generate the data.

July 23, 2012

Compression Units – 2

Filed under: CBO,Exadata,HCC,Indexing,Oracle — Jonathan Lewis @ 4:41 pm BST Jul 23,2012

When I arrived in Edinburgh for the UKOUG Scotland conference a little while ago Thomas Presslie, one of the organisers and chairman of the committee, asked me if I’d sign up on the “unconference” timetable to give a ten-minute talk on something. So I decided to use Hybrid Columnar Compression to make a general point about choosing and testing features. For those of you who missed this excellent conference, here’s a brief note of what I said.

July 20, 2012

Compression Units

Filed under: Exadata,HCC,Oracle — Jonathan Lewis @ 6:04 am BST Jul 20,2012

If you’re starting to work with Exadata you need to work out what how much impact you can have by doing the right (or wrong, or unlucky) sorts of things with the technology. Fortunately there are only a few special features that really need investigation: Hybrid Columnar Compression (HCC), Offloading (and related Smart Scan stuff) and Storage Indexes. These are the features that will have the biggest impact on the space taken up by your data, the volume of data that will move through your system as you load and query it, and the amount of CPU it takes to do something with your data.

There are other features that are important, of course, such as the features for affecting parallel execution, and the options for resource management, but the three I’ve listed above are the core of what’s (currently) unique to Exadata. In this note I’m just going to make a few comments about how Oracle implements HCC, and what side-effects this may have.

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