Hello everybody, I'm experiencing a performance related issue during some validation measurements. Let's first of all clarify what kind of problem I am facing. I've set up a plain tpc-h database without any additional indexes or something like that. To get some performance impressions I wrote a little script that uses 1) pg_ctl to start postgres, 2) executes the same query several times and finally 3) stops the postgres instance using pg_ctl again. These 3 steps are executed several times resulting in varying performance results of which I think that they should be smaller (taking runtime differences I don't have any influence on into account) . Run1: real 0m15.005s user 0m0.000s sys 0m0.000s Run2: real 0m14.012s user 0m0.000s sys 0m0.000s Please be aware that I provided numbers taken from the middle of each run (to exclude any io-related effects), so the buffers are warm, I disabled intels' turbo boost feature and that I have exclusive access to the machine. I used explain (analyze, buffers) to make sure no data has to be loaded from disks during runtime (top and vmstat did not show any movements as well). I flushed the os buffers (no effect regarding performance difference), I disabled autovacuum, I adapted my buffer sizes to hold the whole data required, but I was not able to sort the performance difference out yet. The query I'm currently using is quite easy: select min(l_extendedprice * l_discount * l_tax) from lineitem; Note that I'm aware that my shared_buffer settings has to be bigger than 1/4 of the table to get past the ring buffer. Would be great if anyone could give me some advise where to look at or provide me with some information about postgres performance behaviour. Thank you very much -- View this message in context: http://postgresql.1045698.n5.nabble.com/Varying-performacne-results-after-instance-restart-tp5801717.html Sent from the PostgreSQL - performance mailing list archive at Nabble.com. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
