Re: >1 Virtual Shared Memory Segment slow down

"David L. Kosenko" <davek@informix.com> writes: > > David Williams wrote: > > > > I've been told by Informix that having >1 virtual shared memory > > segment slows down your Informix Online Database server.[snip] > > Why would added more shared memory segments slow down the server > > (they are mapped contiguously but the way)?? > > > > Anything internal to any UNIX kernel which may affect performance? > > > The person that told you this was most likely a bit confused. > > In *general*, there is no problem having more than 1 shared memory > segment, virtual or otherwise. Of course, you don't want to have > more shared memory allocated than you have physical memory, lest > you suffer the ill-effects of a high level of paging. Most systems > suffer no ill-effects having multiple segments. > > There does seem to be some small problem on HP systems. I don't have > the details handy, but as I understand it, only the first few shared > memory segments (I believe the number was 3) are actually cached, and > any additional segments are kept swapped out until particular pages > are needed. It has been a while since I first heard of this, and it > may well have been addressed in later releases of HP/UX. Apparently this still applies to HP-UX 10.10, as we saw significant improvement when we configured a bigger initial segment, thus redusing the number of virtual segments from 6 to 1. -- 'yvind Gjerstad Systems dept Tollpost-Globe AS N-6301 'ndalsnes/Norway E-mail: ogj@it.tollpost.no Phone: +47 7122 6663 Fax: +47 7122 6694