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? 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. 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.) Thanks, KLM Application Developer (And now Performance Tuner, eh?)

Which operating system. Certainly on HP-UX machines this is a big performance increase. On any operating system it will have to 'switch segments' (access another 'item') since each segment can have different access permissions. Keith L Morris wrote in message <39CF8F32.CB0C0F41@wcom.com>... >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? > >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. > >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.) > >Thanks, >KLM >Application Developer (And now Performance Tuner, eh?)