On Tue, 2006-08-01 at 14:22 -0500, Scott Marlowe wrote: > On Tue, 2006-08-01 at 13:59, Aaron Bono wrote: > > On 7/31/06, Thomas Pundt <mlists@xxxxxxxxxxxx> wrote: > > On Monday 31 July 2006 10:06, Aaron Bono wrote: > > | Is there a way I can tell PostgreSQL to give session a low > > priority so even > > | if it does take the full CPU, it only does so if it would > > otherwise be > > | idle? > > > > the "nice" command might do what you want... > > > > > > OK, so I tried: > > > > su - postgres -c "nice -n 19 psql my_db" > > > > The problem is, the psql command has a nice value of 19 but the > > PostgreSQL server process that psql has connected to is running with a > > nice value of 0. My assumption is that, if I then run my functions, > > psql will get low priority but it is the server process that is > > running with normal priority that will still use up all the CPU. > > > > Bottom line, I am skeptical if this will really achieve my goal - to > > have the functions run with low priority. > > > > Is there a way to tell PostgreSQL to change the nice value of a > > particular connection? I guess I could use renice but that means a > > lot of shell scripting to determine what PID to change - I am not a > > shell script expert and would rather not pursue that option. > > This is one of those things that only seems like a good idea at the > time. > > While nice-ing the whole of a postgresql server is doable, nice-ing > individual connections is no advisable. > > You can reach a bad state caused by "priority inversion". Search the > lists (not just admin) for that phrase and you should find out what I > mean. This should probably be a FAQ, as it shows up every few months. I started going down that same road in May... here's the thread from then explaining why it's a bad idea after all: http://archives.postgresql.org/pgsql-performance/2006-05/msg00462.php Bye, Chris.
