RE: Bufwaits and Foreground Writes

See imbedded responses and comments. > -----Original Message----- > From: Obnoxio The Clown [mailto:obnoxio@hotmail.com] > Sent: Friday, December 31, 1999 4:31 AM > To: rbernste@alarismed.com; informix-list@iiug.org > Subject: Re: Bufwaits and Foreground Writes > > > From: "Bernstein, Rick" <rbernste@alarismed.com> > > > >Despite our tuning efforts, we are encountering a > significant number of > >bufwaits and foreground writes > >on our production SAP system. This system runs IDS > 7.30.UC7XK on a 4-way > >RS6000 R50 (AIX). > >I attended Informix's Performance Tuning class last week in > Menlo Park. > >Their suggestions > >included:. > >1) Use different ONCONFIG at different times of the day. > > Our system must be available to online users 24 hours > a day, 6 days a > >week. > > Therefore, this suggestion is not realistic for us. > >2) Reduce the number of LRUs to 4 * number of CPU VPs. > > Will this really help? Or will it make matters worse? > > Utter bollocks. > > >3) Increase the LRU_MIN_DIRTY and LRU_MAX_DIRTY values to > improve write > >cache %. > > This seems equally dumb -- your checkpoints will probably just become > longer. > (snip) > >=>> 'onstat -c' command output follows: (snip) > > >NETTYPE ipcshm,2,30,CPU # Override sqlhosts nettype> parameters > >NETTYPE soctcp,3,45,NET # Override sqlhosts> nettype parameters > > That's not a lot of users, is it? For SAP the number of tcpip connections is based on the application servers' work processes, not end-users. > > >NUMCPUVPS 4 # Number of user (cpu) vps> >083098cl > > You *might* get better performance by adding more CPU VPS > than physical > CPUs. > We are already specifying 4 CPUs on a 4-way machine, despite recommendations to set it to one less than the number of CPUs. The processors are slow on this machine. Therefore, I am hesitant to overload them. > >BUFFERS 150000 # Maximum number of shared buffers> > This seems a bit low for *any* SAP site. Max out, baby, go > for 768,000! :-) This machine only has 1.5 Gbytes of memory. Would not 3 Gbytes (768,000 * 4K) of buffers cause excessive paging? I also need to reserve space for a small application server, Informix virtual storage memory, etc. Any further increases in BUFFERS will likely cause an unacceptable amount of OS paging. We plan to install a new server in a few months. At that time I will increase the number of buffers. > > [SNIP] > > >Thank you for any assistance or insight which you can provide. > > onstat -l? Below is the requested output from onstat -l: Informix Dynamic Server Version 7.30.UC7XK -- On-Line -- Up 3 days 00:44:27 -- 1457264 Kb Physical Logging Buffer bufused bufsize numpages numwrits pages/io P-2 236 256 158253 653 242.35 phybegin physize phypos phyused %used d00035 57287 4163 6475 11.30 Logical Logging Buffer bufused bufsize numrecs numpages numwrits recs/pages pages/io L-3 4 8 3126345 186825 68707 16.7 2.7 Subsystem numrecs Log Space used OLDRSAM 3126345 600996180 address number flags uniqid begin size used %used 333b1a38 1 U-B---- 44208 b00035 5683 5683 100.00 333b1a54 2 U-B---- 44209 2900035 5683 5683 100.00 333b1a70 3 U-B---- 44210 b01668 5683 5683 100.00 333b1a8c 4 U-B---- 44211 2901668 5683 5683 100.00 333b1aa8 5 U-B---- 44212 b02c9b 5683 5683 100.00 333b1ac4 6 U-B---- 44213 2902c9b 5683 5683 100.00 333b1ae0 7 U-B---- 44214 b042ce 5683 5683 100.00 333b1afc 8 U-B---- 44215 29042ce 5683 5683 100.00 333b1b18 9 U-B---- 44216 b05901 5683 5683 100.00 333b1b34 10 U-B---- 44217 2905901 5683 5683 100.00 333b1b50 11 U-B---- 44218 b06f34 5683 5683 100.00 333b1b6c 12 U-B---- 44219 2906f34 5683 5683 100.00 333b1b88 13 U-B---- 44220 b08567 5683 5683 100.00 333b1ba4 14 U-B---- 44221 2908567 5683 5683 100.00 333b1bc0 15 U-B---- 44222 b09b9a 5683 5683 100.00 333b1bdc 16 U-B---L 44223 2909b9a 5683 5683 100.00 333b1bf8 17 U---C-- 44224 b0b1cd 5683 1953 34.37 333b1c14 18 U-B---- 44127 290b1cd 5683 5683 100.00 (snip) 333b24d4 98 U-B---- 44207 29429c5 5683 5683 100.00 ______________________________________________________ > Get Your Private, Free Email at http://www.hotmail.com >