Re: Freeze avoidance of very large table.

On Tue, Jul 7, 2015 at 9:07 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 6 July 2015 at 17:28, Simon Riggs <simon@2ndquadrant.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.

Regards,

--
Masahiko Sawada