Re: System tuning

Jon McNeill sez: > We recently encountered similar sounding performance problems using > Informix 7.11UC2X?? on a HP K400 with 2 processors and 1280M (!) of RAM. > We had almost 99% cache hits, with still extremely sluggish performance. Our > final performance tuning victory came after playing with the NUMCPUVPS, > MULTIPROCESSOR, and SINGLE_CPU_VP parameters in the onconfig file. > > MULTIPROCESSOR 0 > NUMCPUVPS 1 > SINGLE_CPU_VP 1> > gave us stunning performance gains. This two processor system with the above settings outperformed 2,3 & 4 NUMCPUVPS on the same box with 3 and 4 physical CPUs! It seems that the overhead of VCPU synchronization far outweighed benifits of addl VCPUs even with an ADDITIONAL TWO HW PROCESSORS. I also garnered significant gains adjusting SHMVIRTSIZE. The .log file reported seven or eight addl grabs for Shared memory. When consolidated, gains were again measurable. I also measured adjustments to query parallelism parameters (PDQ and DS) and found only degradation when PDQPRIORITY > 0. I beleive that with another SQL mix a differant configuration set (PDQ, NUMCPUVPS >1, etc) would have proved better. Each system MUST be profiled individually. My next task is Extent consolidation. Even with the 99% cache hits that Jon mentions some of these tables are so fragmented that I am betting long that we get more "stunning" gains outta that. 7.11.UC1X2 is the OnLine rev in this system BTW. Enjoy, Mild Bill bburton@us.dhl.com