extra virtual mem segments
We are getting several extra virtual memory segments. Every source I read says to increase SHMVIRTSIZE so that you do not get extra segments. Can someone tell me why its bad to have the extra segments?
Some operating systems, notably HP-UX, have performance issues when trying to handle non-contiguous segments. -- Neil Truby t:01932 724027 Director m:07798 811708 Ardenta Limited e:neil.truby@ardenta.com <asipuleski@ssww.com> wrote in message news:1181849638.271607.28760@e9g2000prf.googlegroups.com... > We are getting several extra virtual memory segments. Every source > I read says to increase SHMVIRTSIZE so that you do not get extra > segments. Can someone tell me why its bad to have the extra segments? >
On Jun 14, 3:33 pm, asipule...@ssww.com wrote: > We are getting several extra virtual memory segments. Every source > I read says to increase SHMVIRTSIZE so that you do not get extra > segments. Can someone tell me why its bad to have the extra segments? On HPUX/PA-RISC platforms having more than 4 shared memory segments causes the 4 special purpose shared memory address registers to thrash dragging performance through the mud. Solaris 9 & 10 perform similar shorthand address translations to improve performance when many processes access the same shared memory segments attached to the same address. If another task attaches to the shared segments at different addresses internally it can/will cause decreased performance across the system due to extrememly high system time usage caused by additional address retranslation overhead. Having many shared memory segments may put your system at risk to run into this 'optimization's side effects. AIX also has some issues with large numbers of shared memory segments. On HPUX/PA-RISC one thing you can do is to use 'RESIDENT -1' in your onconfig file to let the engine consolidate as many of the initial segments as it can into one larger one to reduce the initial count of segments. Beyond that, add up the total size of the extra virtual segments and (unless you know that they were caused by unusual activity) and add the total into SHMVIRTSIZE in the ONCONFIG file for the next restart. Art S. Kagel