On 30 June 2015 at 07:34, Amit Kapila <amit.kapil...@gmail.com> wrote:
> On Tue, Jun 30, 2015 at 11:00 AM, Simon Riggs <si...@2ndquadrant.com> > wrote: > > > > On 30 June 2015 at 05:02, Amit Kapila <amit.kapil...@gmail.com> wrote: > >> > >> On Mon, Jun 29, 2015 at 7:18 PM, Simon Riggs <si...@2ndquadrant.com> > wrote: > >> > > >> > On 28 June 2015 at 17:17, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> >> > >> > If lseek fails badly then SeqScans would give *silent* data loss, > which in my view is worse. Just added pages aren't the only thing we might > miss if lseek is badly wrong. > >> > > >> > >> So for the purpose of this patch, do we need to assume that > >> lseek can give us wrong size of file and we should add preventive > >> checks and other handling for the same? > >> I am okay to change that way, if we are going to have that as assumption > >> in out code wherever we are using it or will use it in-future, otherwise > >> we will end with some preventive checks which are actually not required. > > > > > > They're preventative checks. You always hope it is wasted effort. > > > > I am not sure if Preventative checks (without the real need) are okay if > they > are not-cheap which could happen in this case. I think Validating > buffer-tag > would require rel or sys cache lookup. > True, so don't do that. Keep a list of dropped relations and have the checkpoint process scan the buffer pool every 64 tables, kinda like AbsorbFsync All the heavy lifting gets done in a background process and we know we're safe. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
