Re: Rewriting Free Space Map

Tom Lane wrote:

> The idea that's becoming attractive to me while contemplating the
> multiple-maps problem is that we should adopt something similar to
> the old Mac OS idea of multiple "forks" in a relation.  In addition
> to the main data fork which contains the same info as now, there could
> be one or more map forks which are separate files in the filesystem.

I think something similar could be used to store tuple visibility bits
separately from heap tuple data itself, so +1 to this idea.

(The rough idea in my head was that you can do an indexscan and look
up visibility bits without having to pull the whole heap along; and
visibility updates are also cheaper, whether they come from indexscans
or heap scans.  Of course, the implicit cost is that a seqscan needs to
fetch the visibility pages, too; and the locking is more complex.)

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.