Re: freezing tuples ( was: Why is vacuum_freeze_min_age 100m? )

On Thu, 2009-08-13 at 19:05 -0400, Tom Lane wrote:
> What are you envisioning exactly? If vacuum finds any reason to dirty
> a page (or it's already dirty), then freeze everything on the page that's
> got age > some lower threshold?

Yes. There are two ways to do the threshold:
1. Constant fraction of vacuum_freeze_min_age
2. Extra GUC

I lean toward #1, because it avoids an extra GUC*, and it avoids the
awkwardness when the "lower" setting is higher than the "higher"
setting.

However, #2 might be nice for people who want to live on the edge or
experiment with new values. But I suspect most of the advantage would be
had just by saying that we opportunistically freeze tuples older than
50% of vacuum_freeze_min_age.

Regards,
Jeff Davis

*: As an aside, these GUCs already have incredibly confusing names, and
an extra variable would increase the confusion. For instance, they seem
to use "min" and "max" interchangeably.