Re: Freeze avoidance of very large table.

On Thu, Apr 23, 2015 at 10:42 PM, Robert Haas wrote:
> On Thu, Apr 23, 2015 at 4:19 AM, Simon Riggs  wrote:
>> We only need a freeze/backup map for larger relations. So if we map 1000
>> blocks per map page, we skip having a map at all when size < 1000.
>
> Agreed.  We might also want to map multiple blocks per map slot - e.g.
> one slot per 32 blocks.  That would keep the map quite small even for
> very large relations, and would not compromise efficiency that much
> since reading 256kB sequentially probably takes only a little longer
> than reading 8kB.
>
> I think the idea of integrating the freeze map into the VM fork is
> also worth considering.  Then, the incremental backup map could be
> optional; if you don't want incremental backup, you can shut it off
> and have less overhead.

When I read that I think about something configurable at
relation-level.There are cases where you may want to have more
granularity of this information at block level by having the VM slots
to track less blocks than 32, and vice-versa.
-- 
Michael