On Fri, Aug 12, 2016 at 9:01 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Michael Paquier <michael.paqu...@gmail.com> writes:
>> In short, autovacuum will need to scan by itself the VM of each
>> relation and decide based on that.
> That seems like a worthwhile approach to pursue.  The VM is supposed to be
> small, and if you're worried it isn't, you could sample a few pages of it.
> I do not think any of the ideas proposed so far for tracking the
> visibility percentage on-the-fly are very tenable.

The one visibility map page can store the information of 32672 heap
pages (255MB), but it would be cost if autovacuum scan whole
visibility map for all tables.
So I think that it's better to provide
autovacuum_vacuum_pagevisible_factor as a relopts.
And the autovacuum scans or samples the visibility map of table that
autovacuum_vacuum_pagevisible_factor is set.


Masahiko Sawada

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