Re: ALTER TABLE lock strength reduction patch is unsafe

On Mon, Jan 02, 2012 at 05:09:16PM +0000, Simon Riggs wrote:
> Attached patch makes SnapshotNow into an MVCC snapshot, initialised at
> the start of each scan iff SnapshotNow is passed as the scan's
> snapshot. It's fairly brief but seems to do the trick.

That's a neat trick.  However, if you start a new SnapshotNow scan while one is
ongoing, the primordial scan's snapshot will change mid-stream.