Re: Visibility Groups

On Thu, 2008-08-07 at 10:28 -0400, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > I propose creating "Visibility Groups" that *explicitly* limit the
> > ability of a transaction to access data outside its visibility group(s).
> > By default, visibility_groups would be NULL, implying potential access
> > to all tables.
> 
> I think this would be a lot of mechanism and complication that will go
> completely unused in the field.  It'll be impossible even to explain let
> alone to use effectively, for anyone who's not intensely steeped in the
> details of MVCC.

Yes, but early days.

Given so many people use Oracle currently, I don't think its a stretch
for people to understand internals enough to realise its a Bad Thing.
Developers need to know about serializability and such like to write
correct applications, in some cases.

If not, it's just a simple equationLong Running Statement + Access to Heavily Updated Tables = Bad Thing
so having the ability to prevent access to heavily updated tables helps
to avoid the Bad Thing.

Anyway, the reason for mentioning now was for people to mull on it over
a longer period of time. I have zero interest in any specific user
interface, so that the idea can morph into something that does work,
probably not even written by me. Not pursuing this further right now.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support