On 02/20/2018 09:36 PM, Andres Freund wrote: > Hi, > > On 2018-02-20 21:28:40 +0100, Tomas Vondra wrote: >> I don't quite understand why would this case need the TPC-H tests, or >> why would TPC-H give us more than the very focused tests we've already >> done. > > Because a more complex query shows the cost of changing cache access > costs better than a trivial query. Simplistic queries will often > e.g. not show cost of additional branch predictor usage, because the > branch history is large enough to fit the simple query. But once you go > to a more complex query, and that's not necessarily the case anymore. > > >> The first test was testing a fairly short query where any such >> additional overhead would be much more obvious, compared to the TPC-H >> queries that usually do a lot of other expensive stuff. > > Unfortunately such reasoning IME doesn't work well with cpu-bound stuff. >
OK, point taken. I'll do the tests and report the results. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
