On Tue, Sep 24, 2013 at 6:07 PM, Jeff Janes <jeff.ja...@gmail.com> wrote:
> On Tue, Sep 24, 2013 at 1:13 PM, Daniel Tahara <daniel.tah...@yale.edu>wrote: > >> I am attempting to benchmark a number of queries over a 15GB dataset with >> ~ 10mil records. When I run linux time on the query execution (single >> column projection), it returns 1 minute, but the \timing command returns >> only 15 seconds? >> > > Can you show exactly how you are executing those? > time echo '\\timing \\\\ select msg from test' | $PG_ROOT/bin/psql >> out.txt Here is the actual console output of running the above line four times: Output from Unix time: ~/pgsql/bin/psql test 51.61s user 1.26s system 82% cpu 1:04.08 total ~/pgsql/bin/psql test 50.84s user 1.04s system 83% cpu 1:02.11 total ~/pgsql/bin/psql test 50.32s user 0.79s system 83% cpu 1:01.29 total ~/pgsql/bin/psql test 50.86s user 0.74s system 83% cpu 1:01.53 total Results of \timing: Time: 13423.454 ms Time: 11861.327 ms Time: 11568.109 ms Time: 11292.633 ms > > >> Can someone explain the difference? 1 minute is consistent with reading >> the 15gb from disk at 250mb/s (I have SSDs), but is \timing supposed to >> include that cost? Or simply the computation time plus the time to return >> results. >> > > Probably much of your data is cached in RAM so doesn't have be read from > disk anyway. To the extent it does need to be read from disk, that time > will be included. > shared_buffers are set to default (128mb), as is everything else in postgresql.conf > > psql's \timing doesn't include the time it takes for psql to format and > print the results to the screen (or whereever the output of psql is sent). > Got it. > > Cheers, > > Jeff > Thanks!
