Simon Riggs <si...@2ndquadrant.com> writes:
> On Mon, Jan 2, 2012 at 6:06 PM, Noah Misch <n...@leadboat.com> wrote:
>> On Mon, Jan 02, 2012 at 05:09:16PM +0000, Simon Riggs wrote:
>>> Attached patch makes SnapshotNow into an MVCC snapshot,
>> 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.
> Do we ever do that?
Almost certainly yes. For example, a catcache load may invoke catcache
or relcache reload operations on its way to opening the table or index
needed to fetch the desired row.
I think you can only safely do this if each caller has its own snapshot
variable, a la SnapshotDirty, and that's going to be hugely more
invasive.
regards, tom lane
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