Re: Controlling CPU Usage in PostgreSQL

On Tue, 2006-08-01 at 13:59, Aaron Bono wrote:
> On 7/31/06, Thomas Pundt <mlists@rp-online.de> 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.