PDQ on a single processor system
Jorg Rueschenschmidt asked whether PDQ helps on a single-processor system or whether PDQ_MAXPRIORITY should be set to 0. Neil Truby said multi-core CPUs may benefit but on an old single-core machine context-switching could outweigh gains. scottishpoet said parallel disk access can help, balanced against the ready queue. Andreas Legner warned of memory limits without PDQ and suggested DS_NONPDQ_QUERY_MEM from 10.00 or 9.40. No definitive answer.
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Hi, can sombody tell me if I can benefit from PDQ on single processor system ? According Informix performance guide, multiple treads are started when when PDQ is used, but can i benefit from this wif one physical processor is available only ? I am afraid the extra work to manage the multiple threads will be bad for the overall Informix performance on a single processor system ? Is it better to set PDQ_MAXPRIORITY to 0 in case a single processor system is used ? Any experience ? Regards ... Joerg
Possibly it depends upon your hardware. Multi-cored and multi-threaded processors possibly would benefit from multiple cpu vps, but wih an elderly, single-core, single processor your concern that you may lose more on the swings of conext switching than you gain on the roundabouts of Informix parallel processing may well be founded. -- Neil Truby t:01932 724027 Director m:07798 811708 Ardenta Limited e:neil.truby@ardenta.com "Jörg R'1/4schenschmidt" <jrueschenschmidt@t-online.de> wrote in message news:ehv3q4$1qp$00$1@news.t-online.com... > Hi, > > can sombody tell me if I can benefit from PDQ on single processor system ? > > According Informix performance guide, multiple treads are started when > when PDQ is used, but can i benefit from this wif one physical processor > is available only ? I am afraid the extra work to manage the multiple > threads will be bad for the overall Informix performance on a single > processor system ? > > Is it better to set PDQ_MAXPRIORITY to 0 in case a single processor system > is used ? > > Any experience ? > > Regards ... > > Joerg
I think if you have multiple disks then more then the disks can be accessed in parallel rather than serially. Its then a balance point of how busy the ready Q becomes to process the data returned from the disks 2 disks may be OK, 10 may swamp the the ready Q Jörg RÃ1/4schenschmidt wrote: > Hi, > > can sombody tell me if I can benefit from PDQ on single processor system ? > > According Informix performance guide, multiple treads are started when > when PDQ is used, but can i benefit from this wif one physical processor > is available only ? I am afraid the extra work to manage the multiple > threads will be bad for the overall Informix performance on a single > processor system ? > > Is it better to set PDQ_MAXPRIORITY to 0 in case a single processor > system is used ? > > Any experience ? > > Regards ... > > Joerg
Don't underestimate the memory restrictions when not using PDQ_PRIORITY. Still when using version 10.00 or later 9.40s, DS_NONPDQ_QUERY_MEM can also help out here. Regards, Andreas