On Tue, 2006-01-31 at 21:53 -0800, Luke Lonergan wrote: > Jeffrey, > > On 1/31/06 8:09 PM, "Jeffrey W. Baker" <jwbaker@xxxxxxx> wrote: > >> ... Prove it. > > I think I've proved my point. Software RAID1 read balancing provides > > 0%, 300%, 100%, and 100% speedup on 1, 2, 4, and 8 threads, > > respectively. In the presence of random I/O, the results are even > > better. > > Anyone who thinks they have a single-threaded workload has not yet > > encountered the autovacuum daemon. > > Good data - interesting case. I presume from your results that you had to > make the I/Os non-overlapping (the "skip" option to dd) in order to get the > concurrent access to work. Why the particular choice of offset - 3.2GB in > this case? No particular reason. 8k x 100000 is what the last guy used upthread. > > So - the bandwidth doubles in specific circumstances under concurrent > workloads - not relevant to "Huge Data sets, simple queries", but possibly > helpful for certain kinds of OLTP applications. Ah, but someday Pg will be able to concurrently read from two datastreams to complete a single query. And that day will be glorious and fine, and you'll want as much disk concurrency as you can get your hands on. -jwb
