how compression works -- details

Any details on this? I was at TechEd and heard about it -- a bit. I understand the prefix portion of the compression algorithm and how its placed on the page. But what is the dictionary for? If I found a pre-fix that's common to 3 DIFFERENT values, would it change the prefix or migrate the value to a dictionary? Is the dictionary for cross column compression? When do prefixes and dictionaries get updated -- as soon as the data hits the page? Cool feature, just trying to see how it compares to Oracle.

I assume this will be free? I saw in Oracle 11g they have announced a new Advanced Compression feature, but they took it off the Web site for now -- that would make it $$ now, but it used to be free. Interesting....

[815 byte] By [learningdba] at [2008-2-4]