On 03/06/2015 15:00, Craig Ringer wrote: > > > On 3 June 2015 at 20:04, Andres Freund <and...@anarazel.de > <mailto:and...@anarazel.de>> wrote: > > On 2015-06-03 18:54:24 +0800, Craig Ringer wrote: > > OK, here we go. > > Hm. Wouldn't random sampling be better than what you do? If your queries > have a pattern to them (e.g. you always issue the same 10 queries in > succession), this will possibly only show a subset of the queries. > > I think a formulation in fraction (i.e. a float between 0 and 1) will > also be easier to understand. > > > Could be, yeah. I was thinking about the cost of generating a random > each time, but it's going to vanish in the noise compared to the rest of > the costs in query execution. >
Hello, I've just reviewed the patch. I'm not sure if there's a consensus on the sample rate format. FWIW, I also think a fraction would be easier to understand. Any news about generating a random at each call to avoid the query pattern problem ? The patch applies without error. I wonder if there's any reason for using pg_lrand48() instead of random(), as there's a port for random() if the system lacks it. After some quick checks, I found that auto_explain_sample_counter is always initialized with the same value. After some digging, it seems that pg_lrand48() always returns the same values in the same order, at least on my computer. Have I missed something? Otherwise, after replacing the pg_lrand48() call with a random(), it works just fine. > --- > Craig Ringer http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services -- Julien Rouhaud http://dalibo.com - http://dalibo.org -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
