Rule 1: don’t change anything unless you’re fairly sure the change is going to introduce a reasonable improvement that’s worth the risk. In a production system you may make an index more efficient and “desirable” by rebuilding it with compression, but this may make the optimizer switch to using it in some cases where it should be using another index. This means that an inherently sensible decision actually causes problems if you don’t do a huge amount of testing first.

Rule 2: There is no rule 2, there is only a guideline. The longer the prefix that repeats, the lower the percentage of rows with repeats you need to make the prefix worthwhile; but if the prefix is only a couple of bytes long you need most of the data to have a couple of repeats before it’s likely to be worth compressing.

The best job analysis is always to look at doing a “validate index” on a backup copy of production and then looking at index_stats for the “optimum compression count” and “optimum compression percent saved”, with a quick glance at index_histogram and a check of the data since this may give you some idea of the way in which the repeats occur.

I just saw the event offline. I have a question regarding my existing system which is a medium to large size warehouse. What should be the rule of Thumb when going for Index Compression?
i.e. Only Fact table indexes or Dimension tables or All

Btw i really liked the presentation. I learned a lot form it specially the Visual analysis technique.

Thanks,

The link will take you to a screen with a “Get Webinar Replay” button, and pressing this button will take you to a registration page. After registering, and supplying your email address, you will receive an email that includes buttons to “Watch Now” and “Get Whitepaper”.

If you select the option to watch you get taken through a couple more screens that ask for your name and email address again, you get taken to a screen that allows you to download or watch the webinar. There is a warning that you need to use Internet Explorer 6 with SP1, or later, to view the recording. It’s possible that some other browsers will work – but I chose to get the download (a 20MB zip file) and found that I couldn’t get the extract to run under Google Chrome. Luckily I also had IE6 on the same machine.)

The list of books is on my blog at: http://jonathanlewis.wordpress.com/2009/01/14/books/

I missed all the beginning, arrived for the questions.

Thanks

You mentionned 3-4 books, i did not get the name of the author, could you post some links to those books ?

Thanks

A discovery I made recently is that Google has a convenient “world clock” function, so if you type in “what time {location}” you can get the current time at location. (If you do try this with location = San Francisco, don’t be misled by “San Francisco, Argentina”, I’m aiming for “San Francisco, California” ;) )

Thanks for the comment about the seminar – I’ll have to improve the notes on the last few pages to help the people who have planes to catch.

By the way, thanks for your 2-day presentation in Paris, too bad I miss the end, I tried to solve the last pages of the presentation by myself. But I could find some important clue.. I am still a beginner !!