Thread: pgsql: Document random page cost is only 4x seqeuntial, and not 40x.
Document random page cost is only 4x seqeuntial, and not 40x. Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/c1d9df4fa227781b31be44a5a3024865a7f48049 Modified Files -------------- doc/src/sgml/config.sgml | 20 ++++++++++++++++++++ 1 files changed, 20 insertions(+), 0 deletions(-)
On 14 February 2012 21:55, Bruce Momjian <bruce@momjian.us> wrote: > Document random page cost is only 4x seqeuntial, and not 40x. > > Branch > ------ > master > > Details > ------- > http://git.postgresql.org/pg/commitdiff/c1d9df4fa227781b31be44a5a3024865a7f48049 > > Modified Files > -------------- > doc/src/sgml/config.sgml | 20 ++++++++++++++++++++ > 1 files changed, 20 insertions(+), 0 deletions(-) This change does say that it is 40 times slower: "The default value can be thought of as modeling random access as 40 times slower than sequential..." -- Thom
On Tue, Feb 14, 2012 at 10:44:08PM +0000, Thom Brown wrote: > On 14 February 2012 21:55, Bruce Momjian <bruce@momjian.us> wrote: > > Document random page cost is only 4x seqeuntial, and not 40x. > > > > Branch > > ------ > > master > > > > Details > > ------- > > http://git.postgresql.org/pg/commitdiff/c1d9df4fa227781b31be44a5a3024865a7f48049 > > > > Modified Files > > -------------- > > doc/src/sgml/config.sgml | 20 ++++++++++++++++++++ > > 1 files changed, 20 insertions(+), 0 deletions(-) > > This change does say that it is 40 times slower: > > "The default value can be thought of as modeling random access as 40 > times slower than sequential..." I meant to say that it documents why we have a default of 4x, not 40x. (In fact, real world, it is probably 100x.) -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +
On 14 February 2012 22:46, Bruce Momjian <bruce@momjian.us> wrote: > On Tue, Feb 14, 2012 at 10:44:08PM +0000, Thom Brown wrote: >> On 14 February 2012 21:55, Bruce Momjian <bruce@momjian.us> wrote: >> > Document random page cost is only 4x seqeuntial, and not 40x. >> > >> > Branch >> > ------ >> > master >> > >> > Details >> > ------- >> > http://git.postgresql.org/pg/commitdiff/c1d9df4fa227781b31be44a5a3024865a7f48049 >> > >> > Modified Files >> > -------------- >> > doc/src/sgml/config.sgml | 20 ++++++++++++++++++++ >> > 1 files changed, 20 insertions(+), 0 deletions(-) >> >> This change does say that it is 40 times slower: >> >> "The default value can be thought of as modeling random access as 40 >> times slower than sequential..." > > I meant to say that it documents why we have a default of 4x, not 40x. > (In fact, real world, it is probably 100x.) Hmmm.. okay. I haven't managed to test that myself, but I'll take your word for it. :) -- Thom