Re: Shared Memory Tuning

In <31974E10.54D3@informix.com> Jacques Renaut <jrenaut@informix.com> writes: > >Andrew J. Saville wrote: >> >> Does anybody out there know why Online 7.1 reserves 99% of swap space on >> our HP9000/K400 running HPUX 10.01. We have 640 mb of ram and over 600 >> mb of swap. The shmax parameter is set to it's highest setting possible. Andrew, For 640MB of RAM, I've used at least 2 times that much in swap space, ensuring the swap space is across multiple drives, and if possible, not on any disk channel that the database partitions are on (i.e., using multiple channel RAID controllers, multiple SCSI buses, etc.). One rule of thumb for virtual memory-based operating systems like UNIX recommends approximately 2.5 times RAM as the appropriate swap space size. This model has worked on Informix Online (and PLEXUS/Informix TURBO) in all different industries, systems, UNIX vendors for over 8 years. As much as HP is a respectable company, in large memory situations, I have found early DEC MIPS (DECstations/DECservers) and newer Digital Alpha (AlphaServers) always allowed the most physical memory combined with the faster write-cached and direct paths to memory from the CPU board. (I believe the lowest end DECstation 5000/200 allowed for 480MB of RAM, with the newest AlphaServer 1000s (1GB), and 8400s (4-12GB?) having substantially more RAM available. But that is my opinion. Regarding the Virtual Memory, under heavy load, the 2.5 to 3.2 times RAM is important. In addition, please avoid most hardware vendor's advice to increase buffer space past 10 percent of RAM, or else your high performing CPU will starve for memory and user processes will begin swapping very early on. An update to a ongoing series of virtual memory reports is about ready. Not sure of the distribution channel this time, put will post information for VM-buffs(aka performance tuning/capacity management planners) as soon as I know. This report covered "Big-VM BBSes for mainframe UNIX and mainframe VM/CMS" in 1987, and "Multimedia and Document Imaging Databases on VM-RISC servers" in 1992. Prior distribution agreements prohibit those reports from being placed on the web/Internet at this time. I'm hopeful for the 1997 edition as it focuses on "VM Indicators for Web and Search Engine Performance and Response Time". Since its about the web servers, etc., there is a good chance it'll be available. I'll know in October, and post back [I apologize in advance for this long lead time -- but virtual memory tuning and I go back to the 70s when I was working on early Arpanet activities.] In my experience, proper database memory sizing and capacity planning start with the basics: the first of which is "what is the number of users". This and other factors help determine or at least strongly indicate what is proper amount of RAM/memory, number of disk channels, balanced file systems, multiple swap spaces, etc. These are all critical for database and network throughput within UNIX based environment -- and often overlooked. This is even more important (as the tuning formals change) for blob (data object) spaces for imaging and multimedia. Good luck, Larry Timmins Foresight Technologies, Inc. timmins@ix.netcom.com fax 516-746-4840 voicemail: 516-663-0426