From: | "Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: prefix btree implementation |
Date: | 2005-10-05 19:56:15 |
Message-ID: | di10jf$2jdr$1@news.hub.org |
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Lists: | pgsql-hackers |
"Bricklen Anderson" <BAnderson(at)PresiNET(dot)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
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