On Thu, Sep 3, 2015 at 2:13 PM, Merlin Moncure <mmonc...@gmail.com> wrote: > I find this talk of platters and spindles to be somewhat > baroque; for a 200$ part I have to work pretty hard to max out the > drive when reading and I'm still not completely sure if it's the drive > itself, postgres, cpu, or sata interface bottlenecking me. This will > require a rethink of e_i_o configuration; in the old days there were > physical limitations of the drives that were in the way regardless of > the software stack but we are in a new era, I think. I'm convinced > prefetching works and we're going to want to aggressively prefetch > anything and everything possible. SSD controllers (at least the intel > ones) are very smart.
Wouldn't SSDs need much *less* aggressive prefetching? There's still latency and there are multiple I/O channels so they will still need some. But spinning media gives latencies measured in milliseconds. You can process a lot of tuples in milliseconds. If you have a hundred spindles you want them all busy doing seeks because in the 5ms it takes them to do that you can proess all the results on a single cpu and the rest of time is spend waiting. When your media has latency on the order of microseconds then you only need to have a small handful of I/O requests in flight to keep your processor busy. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
