Tom Lane wrote:
> Jeff Janes <jeff.janes@gmail.com> writes:
> > Of course if you do a full table scan because their are no better
> > options, then it scans sequentially. But you have to scan the pages
> > in *some* order, and it is hard to see how something other than
> > sequential would be systematically better.
>
> In fact, if sequential *isn't* the best order for reading the whole
> file, the filesystem has lost its marbles completely; because that is
> the order in which most files are read, so files ought to be laid out
> on disk (or whatever storage device) to be read most quickly that way.
Plus kernel read-ahead helps with sequential access too because the
kernel can guess the next blocks to be requested --- hard to do that
with random I/O. SSD have fast access but still benefit from
read-ahead.
-- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB
http://enterprisedb.com
+ It's impossible for everything to be true. +
