Re: Proposal for CSN based snapshots

On 06/18/2014 09:12 PM, Robert Haas wrote:
> No.  Otherwise, one of those bits could get changed after a backend
> takes a snapshot and before it finishes using it - so that the
> transaction snapshot is in effect changing underneath it.  You could
> avoid that by memorizing the contents of CLOG when taking a snapshot,
> but that would defeat the whole purpose of CSN-based snapshots, which
> is to make the small and fixed-size.

Ah.

Thankyou. I appreciate the explanation.

-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services