On Fri, Sep 4, 2015 at 05:21:38PM +0100, Greg Stark wrote: > 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.
Well, there is still the processing time of getting that data ready. All I know is that people have reported that prefetching is even more useful for SSDs. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
