Shared Memory challenge on AIX 5.1

One of my sites has 1 Gbyte of RAM. I have configured them to use 512Mbytes of Virtual Shared Memory and about 256 Mbytes of Resident Share Memory. RESIDENT is set to 0. During normal processing everything is OK with those settings. Occasionally the size of the virtual shared memory rises from 512 Mbytes to about 700 Mbytes and there is no effect felt by the users. Last week the Virtual Shared Memory grew from 512 Mbytes to over 1.2 Gbytes in about 90 minutes, but once again there was no discernible effect on the users. Checking with ipcs and onstat -g seg shows that we have 12 virtual shared memory segments. The ONCONFIG parameters are:- SHMVIRTSIZE 524288 SHMADD 65536 SHMTOTAL 0 Should I be concerned at using more shared memory than real memory? regards Malcolm

It will use swap as necessary, it's no big deal as your users didn't (and shouldn't) notice anything. As an aside, why is your SHMADD so small? You must have had a fair few additional segments allocated to be using 1.2Gb. Regards Colin There are 10 types of people in the world, those that understand binary and those that don't >From: "mweallans@panacea.co.uk" <mweallans@panacea.co.uk> >To: informix-list@iiug.org >Subject: Shared Memory challenge on AIX 5.1 >Date: 23 Jan 2006 04:04:10 -0800 > >One of my sites has 1 Gbyte of RAM. I have configured them to use >512Mbytes of Virtual Shared Memory and about 256 Mbytes of Resident >Share Memory. RESIDENT is set to 0. >During normal processing everything is OK with those settings. >Occasionally the size of the virtual shared memory rises from 512 >Mbytes to about 700 Mbytes and there is no effect felt by the users. >Last week the Virtual Shared Memory grew from 512 Mbytes to over 1.2 >Gbytes in about 90 minutes, but once again there was no discernible >effect on the users. Checking with ipcs and onstat -g seg shows that >we have 12 virtual shared memory segments. > >The ONCONFIG parameters are:- >SHMVIRTSIZE 524288 >SHMADD 65536 >SHMTOTAL 0> >Should I be concerned at using more shared memory than real memory? > >regards > >Malcolm > >_______________________________________________ >Informix-list mailing list >Informix-list@iiug.org >http://www.iiug.org/mailman/listinfo/informix-list

Is this operating as 32 or 64 bit? If 32 bit you will run out of shared memory segments on AIX. I recall it to be 11 segments, tho there is some tinkering you can do with the environment variable EXTSHM to increase the number of segments grabbed by SHMADD. >From: "mweallans@panacea.co.uk" <mweallans@panacea.co.uk> >To: informix-list@iiug.org >Subject: Shared Memory challenge on AIX 5.1 >Date: 23 Jan 2006 04:04:10 -0800 > >One of my sites has 1 Gbyte of RAM. I have configured them to use >512Mbytes of Virtual Shared Memory and about 256 Mbytes of Resident >Share Memory. RESIDENT is set to 0. >During normal processing everything is OK with those settings. >Occasionally the size of the virtual shared memory rises from 512 >Mbytes to about 700 Mbytes and there is no effect felt by the users. >Last week the Virtual Shared Memory grew from 512 Mbytes to over 1.2 >Gbytes in about 90 minutes, but once again there was no discernible >effect on the users. Checking with ipcs and onstat -g seg shows that >we have 12 virtual shared memory segments. > >The ONCONFIG parameters are:- >SHMVIRTSIZE 524288 >SHMADD 65536 >SHMTOTAL 0> >Should I be concerned at using more shared memory than real memory? > >regards > >Malcolm > >_______________________________________________ >Informix-list mailing list >Informix-list@iiug.org >http://www.iiug.org/mailman/listinfo/informix-list

Hi, normally yes. It mainly depends on your application and user behaviour, how the access pattern looks like for IDS's SHM. But without knwoing the details (would have to be investigated), swapping of IDS's memory most probably means that you are not far away from thrashing. When the system starts thrashing, then pretty much everything else (on a user or application level) grinds to a virtual halt. The question is, whether the surges in memory usage that you see are due to a general increase in memory usage of existing sessions, a general increase in concurrent sessions (and hence overall memory usage), or whether there are few (or even a single) sessions that suddenly uses that much memory. In the latter two cases you may consider capping the number of user sessions or imposing a limit of memory for individual sessions - for the benefit of the rest. Of course, the easiest may be to buy more memory (e.g. double it) and then not have to worry about it. TIA, Martin -- Martin Fuerderer IBM Informix Development Munich, Germany Information Management informix-list-bounces@iiug.org wrote on 23.01.2006 13:04:10: > One of my sites has 1 Gbyte of RAM. I have configured them to use > 512Mbytes of Virtual Shared Memory and about 256 Mbytes of Resident > Share Memory. RESIDENT is set to 0. > During normal processing everything is OK with those settings. > Occasionally the size of the virtual shared memory rises from 512 > Mbytes to about 700 Mbytes and there is no effect felt by the users. > Last week the Virtual Shared Memory grew from 512 Mbytes to over 1.2 > Gbytes in about 90 minutes, but once again there was no discernible > effect on the users. Checking with ipcs and onstat -g seg shows that > we have 12 virtual shared memory segments. > > The ONCONFIG parameters are:- > SHMVIRTSIZE 524288 > SHMADD 65536 > SHMTOTAL 0> > Should I be concerned at using more shared memory than real memory? > > regards > > Malcolm > > _______________________________________________ > Informix-list mailing list > Informix-list@iiug.org > http://www.iiug.org/mailman/listinfo/informix-list