Le 9 août 2014 05:57, "Ramirez, Danilo" <Danilo.Ramirez@hmhco.com> a écrit : > > Thanks to all for the great info. We are new to postgresql and this discussion has both instructed us and increased our respect for the database and the community. > > I am seeing a behavior that I don’t understand and hopefully you guys can clear it up. > > I am using AWS postgresql db.m3.2xlarge and using pgadmin III 1.18 comparing against AWS oracle on db.m3.2xlarge using sql developer and TOAD. > > I am running a query with 30 tables in the from clause, getting 137 columns back (this is our most basic query, they get a lot more more complex). It returns back 4800 rows. > > In oracle 1st run takes 3.92 seconds, 2nd .38 seconds. Scrolling to end takes and extra 1.5 seconds for total of 5.5. > > Using pgadmin, I run the query. Looking at the lower right hand I can see the time going up. It stops at 8200 ms or close to it every time, then it takes an extra 6 seconds before it displays the rows on the screen. 2nd, 3rd, etc. runs all take about same amount of time 8 sec plus 6 sec > > I then changed it to return only 1 column back. In oracle/sqldeveloper identical behavior as before, same time. In postgresql it now goes down to 1.8 seconds for 1st, 2nd, etc. runs. > > I then change it so that I am asking for the sum of 1 column. In oracle time goes down to .2 seconds and postgresql now goes down to .2 seconds also. > > I then change it back to get the full result set and behavior goes back to original, oracle .38 since its cached, postgresql 8 seconds. >
Are you sure this is postgresql 8 seconds? I'd believe this is more something like postgresql something really low and PgAdmin around 8 seconds displaying it. What I mean is, PgAdmin uses really slow UI components and the time it shows is the time to execute the query and display the data. IOW, you shouldn't use it to benchmark. You should better use psql. Or, much better, you should set log_min_duration_statement to 0 and see exactly how much time postgresql needs to execute it.
yes, try to eliminate a impact of PgAdmin
for this purpose use psql
\timing
\o /dev/null
SELECT ... -- your query
Regards
Pavel
p.s. you can send a plans of slow and fast variants.
