Re: SHMMAX w/ Informix OWS 7.20 and SCO OpenServer 5.0.4

This is the one time I have to disagrea with two of the best and most highly regarded people in c.d.i. If you have less than 640MB RAM in your machine there is hardly any reason to set SHMMAX this high. It's still not that common to have this much memory on an SCO machine. We have been running comfortably for a long time with about 140 MB (up to 30 users) and 256 MB swap (paging) space and SHMMAX at 80MB at one installation. To set it higher than the amount of virtual memory must be meaningless. Some memory allocation error should occur anyway then. Now this is the maximum amount of shared memory that can be used, and the actual used is more interesting. As I have understood it you wouldn't ever want shared memory to be paged out. That would defeat the purpose of it that is mostly for buffers. May be it's still a good idea to set it higher than real memory allows just to avoide an occational situation where more memory may be needed resulting in a crash of the engine. Again as I understand it this should however only happen if you configure things wrongly. If however all that David and Art wants to say is that you need a lot of memory to run Informix engines efficiently, and that you should realy install this much memory in your server it's another discussion. That however depends so much on your application, the amount of data, number of users and so on that there are no general answers. The conclusion is that Informix's suggestion for the SHMMAX parameter is out of place. In the release notes for the engines I have installed the last few years there where also several other kernel parameters that where wrong for SCO, some that must be set but aren't mentioned, some that must be set above the maximum that is specified from SCO without any explanation that this still works and so on. It would have been a good idea for Informix to work a little more on this area. If they did one person at Informix could have done some work instead of every person who have to install the product. On Wed, 03 Jun 1998 13:41:11 -0400, "Art S. Kagel" <kagel@bloomberg.net> wrote: >David Williams wrote: >> >> In article <3573033C.41C6@esd.dl.nec.com>, George Follis >> <follis@esd.dl.nec.com> writes >> >Hello, >> > >> >Trying to install Informix OWS (Online WorkStation?) 7.20 on SCO >> >OpenServer 5.0.4. >> > >> >The 'readme.unx' (dated 11/08/96) says to set the SHMMAX to 671088640 >> >(640MBytes?)! Is this right? I could be a cow/sheep/lemming and >> Correct, follow the readme. You'll regret it otherwise when Informix >> needs more memory and users get errors... >> >> >following the readme, but I prefer to use a more realistic number and >> >also come up with some educated quess to the actual Shared memory size. > >Also the archivers all allocate additional shared memory for themselves >and their subprocesses. The values in the release notes are MINIMUMs. >They are the values that the porting and QA teams found worked for >their testing. For real world applications there is always a chance >that you may need more of some of these resources. For example on our >platform SEMMNI is recommended as 1024 but we have our own applications >using semaphores and have to increase this to 4096. YMMV! > >Art S. Kagel Nils Myklebust NM Data AS Norway E-mail: Nils.Myklebust@nmdata.com FAQ at: http://www.iiug.org/techinfo/faq/faq_top.html (Now with ODBC info under "Third party products".)