Thanks for the reply. On Thu, Feb 25, 2010 at 5:48 PM, Greg Smith <g...@2ndquadrant.com> wrote:
> Yu-Ju Hong wrote: > >> 2. Moreover, the disk utilization was high and the "await" time from >> iostat is around 500 ms. Could disk I/O limit the overall throughput? The >> server has 2 SATA disks, one for system and postgresql and the other is >> dedicated to logging (pg_xlog). As far as I understand, modern database >> systems should be CPU-bound rather than I/O-bound, is it because I did not >> perform adequate performance tuning? >> > > dbt2 is almost exclusively disk I/O bound once the data set gets big > enough. There are some applications where most of the data fits in RAM and > therefore CPU performance is the limiter. dbt2 is exactly the opposite of > such an application though, and the idea that "modern database systems > should be CPU bound" is not really true at all. That's only the case if the > data you're operating on fits in RAM. Otherwise, databases are just as I/O > bound as they've always been. Main thing that's changed is there's a lot > more RAM in systems nowadays. > In my test, there was almost no disk reads (mostly disk writes), so I assumed the size of the database didn't cause the performance bottleneck. Maybe I was wrong. If so, should I increase shared_buffer? Assuming that dbt2 was limited by disk I/O in my experiments, do you think the numbers I got with my server configuration are reasonable? Also, would you mind giving some examples where the applications are CPU bound? That could be useful information to me. > > By the way: a large increase in checkpoint_segments is the first thing you > should do. If you check the database logs, they're probably filled with > complaints about it being too low. 32 would be a useful starting value, > going much higher for a test that's only 10 minutes long is probably > cheating. > > I increased the checkpoint_segments to 10 when I ran the tests. I'll certainly increase it to 32 and give it a try. > -- > Greg Smith 2ndQuadrant US Baltimore, MD > PostgreSQL Training, Services and Support > g...@2ndquadrant.com www.2ndQuadrant.us <http://www.2ndquadrant.us/> > > Thanks, Yu-Ju
