"Bricklen Anderson" <BAnderson@PresiNET.com> wrote
>
> Oracle implements something similar called index compression, but I
> believe it
> is only for common column values. I haven't checked in versions>9r1 so
> maybe
> there are other options implemented by now.
>
> Jonathan Lewis describes some pros and cons here:
> http://www.jlcomp.demon.co.uk/faq/compress_ind.html
>
Oracle 9 uses the grammar like this:
CREATE INDEX ... [ COMPRESS <number_of_first_columns> ]
So it gives the flexibility of choosing optimal number of coulumns to the
user. The script mentioned in the article guesses the optimal number by
estimating the size of each choice. But I am thinking we can do it better:
(1) we don't require that the compressed number of columns on each page are
the same; (2) when we build up index bottom-up, we can determine this number
for each page automatically by maximizing the number of items within a page.
Regards,
Qingqing
