Hello. At Tue, 24 Sep 2019 10:40:19 +0900, Michael Paquier <mich...@paquier.xyz> wrote in <20190924014019.gb2...@paquier.xyz> > On Mon, Sep 23, 2019 at 01:45:14PM +0200, Tomas Vondra wrote: > > On Mon, Sep 23, 2019 at 03:48:50PM +0800, Thunder wrote: > >> Is this an issue? > >> Can we fix like this? > >> Thanks! > >> > > > > I do think it is a valid issue. No opinion on the fix yet, though. > > The report was sent on saturday, so patience ;-) > > And for some others it was even a longer weekend. Anyway, the problem > can be reproduced if you apply the attached which introduces a failure > point, and then if you run the following commands: > create table aa as select 1; > delete from aa; > \! touch /tmp/truncate_flag > vacuum aa; > \! rm /tmp/truncate_flag > vacuum aa; -- panic on standby > > This also points out that there are other things to worry about than > interruptions, as for example DropRelFileNodeLocalBuffers() could lead > to an ERROR, and this happens before the physical truncation is done > but after the WAL record is replayed on the standby, so any failures > happening at the truncation phase before the work is done would be a
Indeed. > problem. However we are talking about failures which should not > happen and these are elog() calls. It would be tempting to add a > critical section here, but we could still have problems if we have a > failure after the WAL record has been flushed, which means that it > would be replayed on the standby, and the surrounding comments are Agreed. > clear about that. In short, as a matter of safety I'd like to think > that what you are suggesting is rather acceptable (aka hold interrupts > before the WAL record is written and release after the physical > truncate), so as truncation avoids failures possible to avoid. > > Do others have thoughts to share on the matter? Agreed for the concept, but does the patch work as described? It seems that query cancel doesn't fire during the holded-off section since no CHECK_FOR_INTERRUPTS() there. regares. -- Kyotaro Horiguchi NTT Open Source Software Center
