Re: Why frequently updated tables are an issue

Jan Wieck wrote:
> On 6/12/2004 3:45 PM, Tom Lane wrote:
>
> > Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
> >> But a per relation bitmap that tells if a block is a) free of dead
> >> tuples and b) all remaining tuples in it are frozen could be used to let
> >> vacuum skip them (there can't be anything to do). The bit would get
> >> reset whenever the block is marked dirty. This would cause vacuum to
> >> look at mainly recently touched blocks, likely to be found in the buffer
> >> cache anyway and thus dramatically reduce the amount of IO and thereby
> >> make high frequent vacuuming less expensive.
> >
> > I don't think it would help very much to define a bit like that --- I
> > can't believe that very many pages would contain only frozen tuples,
> > unless you were to adopt an aggressive policy of using VACUUM FREEZE
> > a lot.
>
> I thought this implies an aggressive policy of freezing everything by
> default. But I guess there is something I am not aware of that makes
> aggressive freezing a bad thing.

Why are frozen tuples significant? I assume any page that has no dead
tuples could be skipped by vacuum.

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