Re: cheaper snapshots redux

Robert Haas <robertmhaas@gmail.com> writes:
> I think the real trick is figuring out a design that can improve
> concurrency.

I'm far from familiar with the detailed concepts here, but allow me to
comment.  I have two open questions:
- is it possible to use a distributed algorithm to produce XIDs,  something like Vector Clocks?
  Then each backend is able to create a snapshot (well, and XID) on its  own, and any backend is still able to compare
itssnapshot to any  other snapshot (well, XID) 
- is it possible to cache the production of the next snapshots so that  generating an XID only means getting the next
ina pre-computed  vector? 
  My guess by reading the emails here is that we need to add some  information at snapshot generation time, it's not
justabout getting  a 32 bit sequence number. 

I'm not sure I'm being that helpful here, but sometime stating the
obviously impossible ideas allows to think about some new design, so I
figured I would still try :)

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support