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Re: cheaper snapshots redux

From: Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: cheaper snapshots redux
Date: 2011-08-23 16:39:30
Message-ID: m2d3fwqdz1.fsf@2ndQuadrant.fr (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)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 its snapshot 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 in a 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 just about 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

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