SSD

There’s never enough time to read everything that’s worth reading, so even though Guy Harrison’s blog is one of the ones worth reading I find that it’s often months since I last read it. Visiting it late last night, I found an interesting batch of articles spread over the last year about the performance of SSD – the conclusions may not be what you expect, but make sure you read all the articles or you might end up with a completely misleading impression:

• Using flash disk for redo on Exadata
• Using SSD for redo on Exadata – pt. 2
• Exadata smart flash logging
• Exadata smart flash logging – outliers

Don’t forget to read the comments as well. For other notes Guy has written about SSD, here’s a URL for his SSD tag.

Compression Units – 5

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 11.2.0.3, 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).

Compression Units – 4

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:

Compression Units – 3

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.

Compression Units – 2

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.

Compression Units

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.

HCC – 2

Just a little follow-up to my previous note on hybrid columnar compression. The following is the critical selection of code I extracted from the trace file after tracing a run of the advisor code against a table with 1,000,000 rows in it:

HCC

Hybrid Columnar Compression is one of the big features of Exadata that can make fairly dramatic differences to the amount of space it takes to store your data. But how do you find out what’s going on under the covers if you haven’t got an Exadata machine in your garage ?

Here’s a simple starting point that occurred to me a couple of days ago after the product manager (or some such) pointed out that there was no need to make an Exadata emulator available to anyone because all you needed was the compression advisor which you could trust because it actually compressed a sample of your data to see how well it could compress.

Exadata

Inevitably there’s still excitement and uncertainty in the air about Exadata – and/or the Database Machine. For ease of reference and a jolly good read I’ve started collecting a few blog postings about it:

Jason Arneil’s Blog

• Category Exadata

Pythian

• Part 1 – mostly hardware
• Part 2 – mostly software
• Part 3 – build and license
• Storage Indexes
• Making the most of Storage indexes
• Making the most of Exadata
• Column limit removed
• What’s in your smart flash cache

Kerry Osborne

• General search list
• Offloading
• Parallel Queuing
• Storage Indexes

Kevin Closson

• Complete catalogue of his many Exadata posts
• A 60 second briefing
• Some interesting statistics
• Critical Analysis meets Exadata (links to 2 videos)

Tanel Poder

• Exadata trouble-shooting article(s)

Uwe Hesse

• Part 1 – Smart Scan
• Part 2 – Storage Indexes
• Part 3 – Compression
• Part 4 – Flash Cache
• Part 5 – Monitoring with Database Control
• Part 6 – Cell Administration with dcli
• Part 7 – Disk Layers
• Important stats and wait events
• Stats collection and smart scan

Arup Nanda

• Introduction to a four-part Exadata command reference

Oracle Official Links

• Oracle Exadata “home page”
• OTN Exadata Forum
• Loading 1TB of data in 20 minutes video – pt 1
• Loading 1TB of data in 20 minutes video – pt 2
• Loading 1TB of data in 20 minutes video – pt 3
• Loading 1TB of data in 20 minutes video – pt 4