On Tue, Dec 3, 2013 at 10:49 AM, Metin Doslu <metin@citusdata.com> wrote: > We have several independent tables on a multi-core machine serving Select > queries. These tables fit into memory; and each Select queries goes over one > table's pages sequentially. In this experiment, there are no indexes or > table joins. > > When we send concurrent Select queries to these tables, query performance > doesn't scale out with the number of CPU cores. We find that complex Select > queries scale out better than simpler ones. We also find that increasing the > block size from 8 KB to 32 KB, or increasing shared_buffers to include the > working set mitigates the problem to some extent. > > For our experiments, we chose an 8-core machine with 68 GB of memory from > Amazon's EC2 service. We installed PostgreSQL 9.3.1 on the instance, and set > shared_buffers to 4 GB.
If you are certain your tables fit in RAM, you may want to disable synchronized sequential scans, as they will create contention between the threads.
