Matthew Wakeling wrote:
Yeb also made the point - there are far too many points on that graph to really tell what the average latency is. It'd be instructive to have a few figures, like "only x% of requests took longer than y".
Average latency is the inverse of TPS. So if the result is, say, 1200 TPS, that means the average latency is 1 / (1200 transactions/second) = 0.83 milliseconds/transaction. The average TPS figure is normally on a more useful scale as far as being able to compare them in ways that make sense to people.
pgbench-tools derives average, worst-case, and 90th percentile figures for latency from the logs. I have 37MB worth of graphs from a system showing how all this typically works for regular hard drives I've been given permission to publish; just need to find a place to host it at internally and I'll make the whole stack available to the world. So far Yeb's data is showing that a single SSD is competitive with a small array on average, but with better worst-case behavior than I'm used to seeing.
-- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
