Re: [HACKERS] Priorities for 6.6

Tom Lane wrote:
> 
> Don Baccus <dhogaza@pacifier.com> writes:
> > While I don't doubt your analysis is correct for the case you've
> > uncovered, it doesn't explain why surrounding a bunch of selects
> > with a begin/end block greatly descreases disk activity for tables
> > that don't change.
> 
> Hmm, I'm not sure why that should be, either.  Anyone?

>From a recent discussion I remember that every block that is read 
in is marked as dirty, regardless of weather it is modified or not.

It is not a genuine bug (as it only slows thong down instead of 
getting wrong results), but still a misfeature.

It is most likely an ancient quickfix for some execution path that 
failed to set the dirty mark when it should have.

---------------------
Hannu