Hi, Should we do full-page write for visibilitymap all the time? Now, when clear visiblitymap, there is no full-page write for vm since we don't save buffer info in insert/update/delete's log.
The full-page write is used to protect pages from disk failure. Without it, 1) set vm: the vm bits that should be set to 1 may still be 0 2) clear vm: the vm bits that should be set to 0 may still be 1 Are these true? Or the page is totally unpredictable? Another question: To address the problem in http://archives.postgresql.org/pgsql-hackers/2010-02/msg02097.php , should we just clear the vm before the log of insert/update/delete? This may reduce the performance, is there another solution? Thanks. -- GaoZengqi pgf...@gmail.com zengqi...@gmail.com On Fri, Mar 25, 2011 at 6:05 AM, Simon Riggs <si...@2ndquadrant.com> wrote: > On Wed, Mar 23, 2011 at 6:16 AM, Jesper Krogh <jes...@krogh.cc> wrote: > > On 2011-03-22 21:43, Robert Haas wrote: > >> > >> I took a crack at implementing the first approach described above, > >> which seems to be by far the simplest idea we've come up with to date. > >> Patch attached. It doesn't seem to be that complicated, which could > >> mean either that it's not that complicated or that I'm missing > >> something. Feel free to point and snicker in the latter case. > > > > Looks simple, but there is now benefit... > > Your tests and discussion remind me that I haven't yet seen any tests > that show that index-only scans would be useful for performance. > > Everyone just seems to be assuming that they make a huge difference, > and that the difference is practically realisable in a common > workload. > > Perhaps that's already been done and I just didn't notice? > > -- > Simon Riggs http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers >
