Re: HOT patch - version 15

Bruce Momjian wrote:
> Looking at the patch I see:
> 
> +       /*
> +        * Mark the page as clear of prunable tuples. If we find a tuple which
> +        * may become prunable, we shall set the hint again.
> +        */
> +       PageClearPrunable(page);
> 
> I like the idea of the page hint bit, but my question is if there is a
> long-running transaction, isn't each SELECT going to try to defragment a
> page over and over again because there is still something prunable on
> the page?

Maybe that risk could be lowered if instead of a flag, we stored the
minimal global xmin needed to prune at least one tuple.

greetings, Florian Pflug