Hello, At Wed, 22 Apr 2015 21:59:27 +0200, Andomar <andomar@xxxxxxxx> wrote in <5537FD9F.3060109@xxxxxxxx> > > Looping through 384 index scans of tbl, each taking 0.040 ms. > > That's 15.36 ms. That leaves 0.291 ms unaccounted for, which means > > that's about how much time the top level nested loop took to do its > > work. > > > > Thanks for your reply, interesting! I'd have thought that this line > actually implied 0 ms: > > actual time=0.040..0.040 > > But based on your reply this means, it took between 0.040 and 0.040 ms > for each loop? You might mistake how to read it (besides the scale:). The index scan took 40ms as the average through all loops. The number at the left of '..' is "startup time". http://www.postgresql.org/docs/9.4/static/sql-explain.html # Mmm.. this doesn't explain about "startup time".. It's the time # taken from execution start to returning the first result. At Wed, 22 Apr 2015 14:18:40 -0600, Jason Petersen <jason@xxxxxxxxxxxxx> wrote in <4FB6E62B-3876-4D5C-9737-52F23D6693B6@xxxxxxxxxxxxx> > > On Apr 22, 2015, at 1:59 PM, Andomar <andomar@xxxxxxxx> wrote: > > > > Is there a way to tell postgres that a function will always return the same result for the same parameter, within the same transaction? > > Yup… read over the Function Volatility Categories > <http://www.postgresql.org/docs/9.4/static/xfunc-volatility.html> > page and decide which you need. What you’re describing is > STABLE (or slightly stricter than STABLE, since STABLE makes > that guarantee only for a single statement within a > transaction). And you will see what volatility category does a function go under in pg_proc system catalog. =# select proname, provolatile from pg_proc where oid = 'random'::regproc; proname | provolatile ---------+------------- random | v random() is a volatile funciton. http://www.postgresql.org/docs/9.4/static/catalog-pg-proc.html regards, -- Kyotaro Horiguchi NTT Open Source Software Center -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
