Re: removing PD_ALL_VISIBLE

On Fri, May 31, 2013 at 10:28:12AM -0700, Josh Berkus wrote:
> 
> >> Isn't the visibility map already required for proper return results as
> >> we use it for index-only scans.  I think the optimization-only ship has
> >> sailed.
> > 
> > At the moment we can remove it without causing corruption. If we were to
> > use it for freezing we couldn't anymore. So there's a difference - how
> > big it is I am not sure.
> 
> Depends on your definition of corruption, really.
> 
> But yes, right now, the vismap can lose bits without causing any
> corruption, and making all-frozen depend on it would eliminate that.

Roberts statement was:

> Loss or corruption of a single visibility map page means possible loss
> of half a gigabyte of data.

Certainly unidentified corruption of a visibility map page could easily
cause incorrect results.  So, technically, _adding_ bits would cause
corruption.


--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +