| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndQuadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Atri Sharma <atri(dot)jiit(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe |
| Date: | 2014-03-04 22:39:01 |
| Message-ID: | 20140304223901.GD27273@alap3.anarazel.de |
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| Thread: | |
| Lists: | pgsql-hackers |
On 2014-03-04 14:29:31 -0800, Josh Berkus wrote:
> On 03/04/2014 11:43 AM, Andres Freund wrote:
> > On March 4, 2014 8:39:55 PM CET, Simon Riggs <simon(at)2ndQuadrant(dot)com> wrote:
> >> I was going to add an option to increase lock level, but I can't see
> >> why you'd want it even. The dumps are consistent...
> >
> > Mvcc scans only guarantee that individual scans are consistent, not that separate scans are. Each individual scan takes a new snapshot if there's been ddl.
> I thought that we were sharing the same snapshot, for parallel dump?
That snapshot is about data, not the catalog. And no, we can't easily
reuse one for the other, see elsewhere in this thread for some of the
reasons.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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