Re: Converting MySQL tinyint to PostgreSQL

On Tue, Jul 19, 2005 at 11:48:16AM +0200, Martijn van Oosterhout wrote:
> int, bool, bool     6 bytes, no padding
> bool, int, bool     9 bytes, including 3 bytes padding
> bool, bool, int     8 bytes, including 2 bytes padding
We store bool's in a byte and don't compact? That would be another very
handy change... the first 8 bools in a table all use one byte, the next
8 use another, etc.

> Assuming an int is 4 bytes. If it's 8-bytes it's even more obvious.
>
> I think it would be a really good for postgresql to reorder the fields
> in the background (on disk, not in select * statements).

I believe the last time this was discussed the consensus was that we
should first have a way for users to do this manually, since the backend
would need most of that framework anyway. I don't know that much (if
any) work has been done on this.

One of the advantages of divorcing the in-memory page layout from the
on-disk page layout is that by doing so you get even more benefit from
re-ordering fields, and it's not dependant on figuring out how to
present fields in a different order than how they're stored in the page.
The downside is that it doesn't get you some of the in-memory benefits
that field ordering will get you, but I suspect in most cases the
on-disk gains will swamp those out anyway.

Does anyone have any idea what it would take to hack in divorcing disk
page layout from memory layout just for testing?
--
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