Re: opportunistic tuple freezing

I assume no progress has been made on testing the performance of this
patch.


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Jeff Davis wrote:
> Attached is a patch to implement the idea discussed here:
> 
> http://archives.postgresql.org/pgsql-hackers/2009-08/msg01137.php
> 
> If VACUUM freezes one tuple on a page, it's likely that there are others
> on the same page that are close to vacuum_freeze_min_age, but not quite.
> Because the page is already dirty from freezing one tuple, it makes
> sense to be more aggressive about freezing the rest, in the hope that
> all the tuples will be frozen, and we will not have to dirty the page
> again later.
> 
> This patch introduces a GUC vacuum_freeze_opportunistic_ratio. If one
> tuple on a page is frozen by vacuum, it effectively multiplies
> vacuum_freeze_min_age by vacuum_freeze_opportunistic_ratio and uses that
> lower (more aggressive) value only for the current page.
> 
> The reason we don't just freeze all the tuples we can (effectively
> setting the vacuum_freeze_opportunistic_ratio to zero) is to preserve
> transaction ID information for diagnosing problems.
> 
> Regards,
>     Jeff Davis

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