On 19-1-2010 13:59 Willy-Bas Loos wrote:
Hi, I have a query that runs for about 16 hours, it should run at least weekly. There are also clients connecting via a website, we don't want to keep them waiting because of long DSS queries. We use Debian Lenny. I've noticed that renicing the process really lowers the load (in "top"), though i think we are I/O bound. Does that make any sense?
Renicing a postgresql-process can be a very bad thing for the throughput. As it may also possess some locks, which are required by the processes that you think should have a higher priority. Those higher priority processes will be locked by the lower priority one.
Then again, renicing postgresql as a whole can be useful. And if your absolutely certain you want to renice a process, renicing a process shouldn't break anything. But it may have some unexpected side effects.
Another command to look at, if you're I/O-bound, is the 'ionice' command, which is similar to nice, but obviously intended for I/O. For some I/O-bound background job, one of the 'idle' classes can be a nice level. But for a (single) postgres-process, I'd be careful again for the same reasons as with process-nice.
To see which commands do some I/O, looking at 'iotop' may be useful, apart from just examining the output of 'iostat' and similar commands.
Best regards, Arjen -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
