Robert Haas wrote: > On Wed, Jun 15, 2016 at 1:44 PM, Kevin Grittner <kgri...@gmail.com> > wrote:
> > The test I showed creates a situation which (to ANALYZE) is > > identical to what you describe -- ANALYZE sees a page with an LSN > > recent enough that it could have been (and actually has been) > > pruned. Why would it be better for the ANALYZE to fail than to > > complete? > > As I understand it, the reason we need to sometimes give "ERROR: > snapshot too old" after early pruning is because we might otherwise > give the wrong answer. So what constitutes "the wrong answer"? A regular transaction reading a page and not finding a tuple that should have been there but was removed, is a serious problem and should be aborted. For ANALYZE it may not matter a great deal. Some very old tuple that might have been chosen for the sample is not there; a different tuple is chosen instead, so the stats might be slightly difference. No big deal. Maybe it is possible to get into trouble if you're taking a sample for an expression index. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
