On Mon, May 30, 2016 at 4:22 PM, Alex Ignatov <a.igna...@postgrespro.ru> wrote:
> > _____________________________ > From: Scott Marlowe <scott.marl...@gmail.com> > Sent: Monday, May 30, 2016 20:14 > Subject: Re: [GENERAL] Silent data loss in its pure form > To: Alex Ignatov <a.igna...@postgrespro.ru> > Cc: <pgsql-general@postgresql.org> > > > > On Mon, May 30, 2016 at 10:57 AM, Alex Ignatov <a.igna...@postgrespro.ru> > wrote: > > Following this bug reports from redhat > > https://bugzilla.redhat.com/show_bug.cgi?id=845233 > > > > it rising some dangerous issue: > > > > If on any reasons you data file is zeroed after some power loss(it is the > > most known issue on XFS in the past) when you do > > select count(*) from you_table you got zero if you table was in one > > 1GB(default) file or some other numbers !=count (*) from you_table before > > power loss > > No errors, nothing suspicious in logs. No any checksum errors. Nothing. > > > > Silent data loss is its pure form. > > > > And thanks to all gods that you notice it before backup recycling which > > contains good data. > > Keep in mind it while checking you "backups" in any forms (pg_dump or the > > more dangerous and short-spoken PITR file backup) > > > > You data is always in danger with "zeroed data file is normal file" > > paradigm. > > That bug shows as having been fixed in 2012. Are there any modern, > supported distros that would still have it? It sounds really bad btw. > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general > > It is not about modern distros it is about possible silent data loss in > old distros. We have replication, have some form of data check summing, but > we are powerless in front of this XFS bug just because "zeroed file is you > good friend in Postgres". > With "zero file is good file" paradigm and this noted XFS bug PG as it > is now is "colossus with feet of clay" It can do many things but it cant > even tell us that we have some trouble with our precious data. > No need to prevent or to some other AI magic and so on when zero doom day > has come. > What we need now is some error report about suspicious zeroed file. To > make us sure that something went wrong and we have to do recovery. > Today PG "power loss" recovery and this XFS bug poisoning our ensurance > that recovery went well . It went well even with zeroed file. It it not > healthy behavior. It like a walk on a mine field with eyes closed. > I think it is very dangerous view on data to have data files without any > header in it and without any files checking at least on PG start. > With this known XFS bug it can leads to undetected and unavoidable loss > of data. > For those not following -general this is basically an extension of the following thread. "Deleting a table file does not raise an error when the table is touched afterwards, why?" https://www.postgresql.org/message-id/flat/184509399.5590018.1464622534207.javamail.zim...@dbi-services.com#184509399.5590018.1464622534207.javamail.zim...@dbi-services.com David J.
