Re: Index Tuple Compression Approach?

Isn't this what Grouped Index Tuples is?

On Tue, Aug 14, 2007 at 05:21:16PM -0400, Chris Browne wrote:
> I recently had a chat with someone who was pretty intimate with Adabas
> for a number of years who's in the process of figuring things out
> about PostgreSQL. We poked at bits of the respective implementations,
> seeing some similarities and differences. He pointed out one aspect
> of index handling that could (in principle) be an interesting
> optimization.
>
> Evidently, in Adabas, index leaf nodes were not simply tuples, but
> lists where the index value would not be repeated.
>
> In PostgreSQL, if you have the index value 'abc', and there are 10
> tuples with that value, then you'll have a page full of tuples of the
> following form:
>
> |abc|ptr[rec1]|abc|ptr[rec2]|abc|ptr[rec3]| ...and so forth...
>
> Now, the Adabas approach was rather different. It would only have the
> index value once, and then have the list of tuple pointers:
>
> |abc|ptr[rec1],ptr[rec2],ptr[rec3],...[ptr[rec10]|
>
> This could allow a fair bit of compression, for cases where the index
> value is not unique.
>
> There is a concommitant downside, that concurrent updates may fight
> over a page, and, since there would be a higher density, there would
> be more need to fight over pages.
>
> Does this seem pretty much like madness? Or is it a plausible "some
> day ToDo"?
> --
> "cbbrowne","@","acm.org"
> http://linuxfinances.info/info/postgresql.html
> "I don't do drugs anymore 'cause I find I get the same effect just by
> standing up really fast." -- Jonathan Katz
>
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--
Decibel!, aka Jim Nasby decibel(at)decibel(dot)org
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