On Friday, January 06, 2012 08:53:38 PM Robert Haas wrote: > On Fri, Jan 6, 2012 at 2:48 PM, Andres Freund <and...@anarazel.de> wrote: > > On Friday, January 06, 2012 08:45:45 PM Heikki Linnakangas wrote: > >> On 06.01.2012 20:26, Simon Riggs wrote: > >> > The following patch (v4) introduces a new WAL record type that writes > >> > backup blocks for the first hint on a block in any checkpoint that has > >> > not previously been changed. IMHO this fixes the torn page problem > >> > correctly, though at some additional loss of performance but not the > >> > total catastrophe some people had imagined. Specifically we don't need > >> > to log anywhere near 100% of hint bit settings, much more like 20-30% > >> > (estimated not measured). > >> > >> How's that going to work during recovery? Like in hot standby. > > > > How's recovery a problem? Unless I miss something that doesn't actually > > introduce a new possibility to transport hint bits to the standby (think > > fpw's). A new transport will obviously increase traffic but ... > > The standby can set hint bits locally that weren't set on the data it > received from the master. This will require rechecksumming and > rewriting the page, but obviously we can't write the WAL records > needed to protect those writes during recovery. So a crash could > create a torn page, invalidating the checksum. Err. Stupid me, thanks.
> Ignoring checksum errors during Hot Standby operation doesn't fix it, > either, because eventually you might want to promote the standby, and > the checksum will still be invalid. Its funny. I have the feeling we all are missing a very obvious brilliant solution to this... Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
