On Thursday, December 01, 2011 03:11:43 PM Robert Haas wrote: > On Thu, Dec 1, 2011 at 4:09 AM, Andres Freund <and...@anarazel.de> wrote: > >> Oh, that's interesting. Why do you want to avoid frequent fsyncs? I > >> thought the point of synchronous_commit=off was to move the fsyncs to > >> the background, but not necessarily to decrease the frequency. > > > > Is that so? If it wouldn't avoid fsyncs how could you reach multiple > > thousand TPS in a writing pgbench run on a pretty ordinary system with > > fsync=on? > Eh, well, what would stop you from achieving that? An fsync operation > that occurs in the background doesn't block further transactions from > completing. But it will slow down overall system io. For one an fsync() on linux will cause a queue drain on the io submit queue. For another it counts against the total available random io ops a device can do. Which in turn will cause slowdown for anything else doing syncronous random io. I.e. read(2).
> Meanwhile, getting the WAL records on disk faster allows > us to set hint bits sooner, which is a significant win, as shown by > the numbers I posted upthread. Oh, that part I dont doubt. Sorry for that. Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
