RE: SHMVIRTSIZE --- How much bang for the buck?

> -----Original Message----- > From: Keith L Morris [mailto:keith.l.morris@wcom.com] > Sent: Monday, September 25, 2000 12:51 PM > To: informix-list@iiug.org > Subject: SHMVIRTSIZE --- How much bang for the buck? > > > Greetings, > > On a current production system I have found an instance that has 8 > VIRTUAL segments. > > (onstat -g seg) > > The main segment is 400 meg and the other 7 are 200 meg each. > (1.8 Gig > total) > > The /etc/system (solaris) allows 2 Gig shared memory segments. > > I'm thinking that since we use the memory ANYWAY we should > consolidate, > and the Informix manuals agree. > > QUESTION: > > Will I see any performance increase by doing this? While I'm not sure how Solaris handles shared memory segments, I KNOW that this could be a major issue for HPUX. In my early years as DBA, I allowed Informix to allocate extra SHM segments. When I consolidated the 'extra' segments unti SHMVIRTSIZE, I saw an immediate 40% performance boost in our batch reporting. > > Is this related to CPU context switching in any way? (This > box's does 2 > times more context switching than it does sytem calls.) I > think that's > a bit too much. Other boxes I have do 25%.... that seems more normal > than 200%. > > Anyway, I figure regardless of the context switching answer... the > consolidation of the segments couldn't hurt. > Agreed. Less overhead for the OS in the memory management area, it seems. > Would it help the database to increase the operating system's max for > shared memory to 4 Gig instead of 2 Gig? (We have 16 Gig total memory > and the database is the MAIN application.) > Not sure. How are your BUFFERS currently set?