Re: Do I need to be RESIDENT

Platform is Solaris 9, 16CPU, 32Gb memory Regards Colin >From: Michael Mueller <m.mueller01.delete_me@kay-mueller.de> >To: Colin Dawson <cjd_1955@hotmail.com> >Subject: Re: Do I need to be RESIDENT >Date: Wed, 30 Mar 2005 14:39:08 +0200 > >What platform are you on? > >Making memory resident that is not paged out anyway may not make sense. But >on Solaris the "RESIDENT -1" setting has a second effect: It creates shared >memory with a page size of 4 MB instead of 8k pages (using the >SHM_SHARE_MMU flag of shmat()). This speeds up physical to virtual page >translation in the cpu and has a performance benefit on large systems. > >Michael > >Colin Dawson wrote: >>We currently have RESIDENT set to -1, if I increase BUFFERS above 2M I get >>the message >> >>07:55:17 Informix Dynamic Server Stopped. >>07:56:49 mt_shm_init: can't create resident segment>> >>When I change RESIDENT to 0, I can increase the buffers to whatever I >>want. I know why I'm getting this error, that is not the reason for this >>posting. What I'm looking for is an informed opinion of why set RESIDENT >>to -1 in the first place, Is there a real benefit or only a percieved one? >> >> >> >> >> >>Regards >> >>Colin Dawson >> >> >>sending to informix-list > sending to informix-list

In this case I would expect a real benefit. The operating system has to manage every single page of shared memory and has to store and cache address mappings for every page. Setting "RESIDENT -1" on Solaris means reducing the number of pages by a factor of 512. I also know a case of a comparable system where "onmode -k" and onstat commands became slow until "RESIDENT -1" was used. This was presumably caused by the operating system because detaching so many pages of memory was a major task. Michael Colin Dawson wrote: > Platform is Solaris 9, 16CPU, 32Gb memory > > > > Regards > > Colin > > > > > > >>From: Michael Mueller <m.mueller01.delete_me@kay-mueller.de> >>To: Colin Dawson <cjd_1955@hotmail.com> >>Subject: Re: Do I need to be RESIDENT >>Date: Wed, 30 Mar 2005 14:39:08 +0200 >> >>What platform are you on? >> >>Making memory resident that is not paged out anyway may not make sense. But >>on Solaris the "RESIDENT -1" setting has a second effect: It creates shared >>memory with a page size of 4 MB instead of 8k pages (using the >>SHM_SHARE_MMU flag of shmat()). This speeds up physical to virtual page >>translation in the cpu and has a performance benefit on large systems. >> >>Michael >> >>Colin Dawson wrote: >> >>>We currently have RESIDENT set to -1, if I increase BUFFERS above 2M I get >>>the message >>> >>>07:55:17 Informix Dynamic Server Stopped. >>>07:56:49 mt_shm_init: can't create resident segment>>> >>>When I change RESIDENT to 0, I can increase the buffers to whatever I >>>want. I know why I'm getting this error, that is not the reason for this >>>posting. What I'm looking for is an informed opinion of why set RESIDENT >>>to -1 in the first place, Is there a real benefit or only a percieved one? >>> >>> >>> >>> >>> >>>Regards >>> >>>Colin Dawson >>> >>> >>>sending to informix-list >> > > > sending to informix-list