Re: Freeze avoidance of very large table.

On Mon, Jul 13, 2015 at 3:39 PM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>
wrote:
>
> On Tue, Jul 7, 2015 at 9:07 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On 6 July 2015 at 17:28, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> >
> >> I think we need something for pg_upgrade to rewrite existing VMs.
> >> Otherwise a large read only database would suddenly require a massive
> >> revacuum after upgrade, which seems bad. That can wait for now until
we all
> >> agree this patch is sound.
> >
> >
> > Since we need to rewrite the "vm" map, I think we should call the new
map
> > "vfm"
> >
> > That way we will be able to easily check whether the rewrite has been
> > conducted on all relations.
> >
> > Since the maps are just bits there is no other way to tell that a map
has
> > been rewritten
>
> To avoid revacuum after upgrade, you meant that we need to rewrite
> each bit of vm to corresponding bits of vfm, if it's from
> not-supporting vfm version(i.g., 9.5 or earlier ). right?
> If so, we will need to do whole scanning table, which is expensive as
well.
> Clearing vm and do revacuum would be nice, rather than doing in
> upgrading, I think.
>

How will you ensure to have revacuum for all the tables after
upgrading? Till the time Vacuum is done on the tables that
have vm before upgrade, any queries on those tables can
become slower.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com